β¨ samber/lo
is a Lodash-style Go library based on Go 1.18+ Generics.
This project started as an experiment with the new generics implementation. It may look like Lodash in some aspects. I used to code with the fantastic "go-funk" package, but "go-funk" uses reflection and therefore is not typesafe.
As expected, benchmarks demonstrate that generics will be much faster than implementations based on the "reflect" package. Benchmarks also show similar performance gains compared to pure for
loops. See below.
In the future, 5 to 10 helpers will overlap with those coming into the Go standard library (under package names slices
and maps
). I feel this library is legitimate and offers many more valuable abstractions.
See also:
- samber/do: A dependency injection toolkit based on Go 1.18+ Generics
- samber/mo: Monads based on Go 1.18+ Generics (Option, Result, Either...)
Why this name?
I wanted a short name, similar to "Lodash" and no Go package currently uses this name.
go get github.com/samber/lo@v1
This library is v1 and follows SemVer strictly.
No breaking changes will be made to exported APIs before v2.0.0.
You can import lo
using:
import (
"github.com/samber/lo"
lop "github.com/samber/lo/parallel"
)
Then use one of the helpers below:
names := lo.Uniq[string]([]string{"Samuel", "Marc", "Samuel"})
// []string{"Samuel", "Marc"}
Most of the time, the compiler will be able to infer the type so that you can call: lo.Uniq([]string{...})
.
GoDoc: https://godoc.org/github.com/samber/lo
Supported helpers for slices:
- Filter
- Map
- FilterMap
- FlatMap
- Reduce
- ForEach
- Times
- Uniq
- UniqBy
- GroupBy
- Chunk
- PartitionBy
- Flatten
- Shuffle
- Reverse
- Fill
- Repeat
- RepeatBy
- KeyBy
- Drop
- DropRight
- DropWhile
- DropRightWhile
- Reject
- Count
- CountBy
- Subset
- Slice
- Replace
- ReplaceAll
- Compact
Supported helpers for maps:
- Keys
- Values
- PickBy
- PickByKeys
- PickByValues
- OmitBy
- OmitByKeys
- OmitByValues
- Entries / ToPairs
- FromEntries / FromPairs
- Invert
- Assign (merge of maps)
- MapKeys
- MapValues
Supported math helpers:
Supported helpers for strings:
Supported helpers for tuples:
Supported intersection helpers:
- Contains
- ContainsBy
- Every
- EveryBy
- Some
- SomeBy
- None
- NoneBy
- Intersect
- Difference
- Union
- Without
- WithoutEmpty
Supported search helpers:
- IndexOf
- LastIndexOf
- Find
- FindIndexOf
- FindLastIndexOf
- FindKey
- FindKeyBy
- FindUniques
- FindUniquesBy
- FindDuplicates
- FindDuplicatesBy
- Min
- MinBy
- Max
- MaxBy
- Last
- Nth
- Sample
- Samples
Conditional helpers:
Type manipulation helpers:
Function helpers:
Concurrency helpers:
Error handling:
Constraints:
- Clonable
Iterates over a collection and returns an array of all the elements the predicate function returns true
for.
even := lo.Filter[int]([]int{1, 2, 3, 4}, func(x int, _ int) bool {
return x%2 == 0
})
// []int{2, 4}
Manipulates a slice of one type and transforms it into a slice of another type:
import "github.com/samber/lo"
lo.Map[int64, string]([]int64{1, 2, 3, 4}, func(x int64, _ int) string {
return strconv.FormatInt(x, 10)
})
// []string{"1", "2", "3", "4"}
Parallel processing: like lo.Map()
, but the mapper function is called in a goroutine. Results are returned in the same order.
import lop "github.com/samber/lo/parallel"
lop.Map[int64, string]([]int64{1, 2, 3, 4}, func(x int64, _ int) string {
return strconv.FormatInt(x, 10)
})
// []string{"1", "2", "3", "4"}
You also can control the conurrency limit by optional ParallelOption to limit the maximum number of concurrent iteratee
goroutines running at the same time.
lop.Map(list, iteratee, lop.WithConcurrency(20)) // up to 20 concurrent goroutines running at the same time
Manipulates a slice of one type and transforms it into a slice of another type. Short circuits and returns an error if the mapper function returns an error:
import "github.com/samber/lo"
x, err := lo.MapWithError[int64, string]([]int64{1, 2, 3, 4}, func(x int64, _ int) (string, error) {
if x == 5 {
return nil, errors.New("x is 5")
}
return strconv.FormatInt(x, 10), nil
})
// []string{"1", "2", "3", "4"}
// nil
x, err := lo.MapWithError[int64, string]([]int64{1, 2, 3, 4}, func(x int64, _ int) (string, error) {
if x == 4 {
return nil, errors.New("x is 4")
}
return strconv.FormatInt(x, 10), nil
})
// nil
// error "x is 4"
Parallel processing: like lo.MapWithError()
, but the mapper function is called in a goroutine. Parallel processing is cancelled on first encountered error.
import lop "github.com/samber/lo/parallel"
x, err := lop.MapWithError[int64, string]([]int64{1, 2, 3, 4}, func(x int64, _ int) (string, error) {
if x == 4 {
return nil, errors.New("x is 4")
}
return strconv.FormatInt(x, 10), nil
})
// nil
// error "x is 4"
Manipulates a slice and transforms and flattens it to a slice of another type.
lo.FlatMap[int, string]([]int{0, 1, 2}, func(x int, _ int) []string {
return []string{
strconv.FormatInt(x, 10),
strconv.FormatInt(x, 10),
}
})
// []string{"0", "0", "1", "1", "2", "2"}
Returns a slice which obtained after both filtering and mapping using the given callback function.
The callback function should return two values: the result of the mapping operation and whether the result element should be included or not.
matching := lo.FilterMap[string, string]([]string{"cpu", "gpu", "mouse", "keyboard"}, func(x string, _ int) (string, bool) {
if strings.HasSuffix(x, "pu") {
return "xpu", true
}
return "", false
})
// []string{"xpu", "xpu"}
Manipulates a slice and transforms and flattens it to a slice of another type.
lo.FlatMap[int, string]([]int{0, 1, 2}, func(x int, _ int) []string {
return []string{
strconv.FormatInt(x, 10),
strconv.FormatInt(x, 10),
}
})
// []string{"0", "0", "1", "1", "2", "2"}
Reduces a collection to a single value. The value is calculated by accumulating the result of running each element in the collection through an accumulator function. Each successive invocation is supplied with the return value returned by the previous call.
sum := lo.Reduce[int, int]([]int{1, 2, 3, 4}, func(agg int, item int, _ int) int {
return agg + item
}, 0)
// 10
Iterates over elements of a collection and invokes the function over each element.
import "github.com/samber/lo"
lo.ForEach[string]([]string{"hello", "world"}, func(x string, _ int) {
println(x)
})
// prints "hello\nworld\n"
Parallel processing: like lo.ForEach()
, but the callback is called as a goroutine.
import lop "github.com/samber/lo/parallel"
lop.ForEach[string]([]string{"hello", "world"}, func(x string, _ int) {
println(x)
})
// prints "hello\nworld\n" or "world\nhello\n"
You also can control the conurrency limit by optional ParallelOption to limit the maximum number of concurrent iteratee
goroutines running at the same time.
lop.ForEach(list, iteratee, lop.WithConcurrency(20)) // up to 20 concurrent goroutines running at the same time
Times invokes the iteratee n times, returning an array of the results of each invocation. The iteratee is invoked with index as argument.
import "github.com/samber/lo"
lo.Times[string](3, func(i int) string {
return strconv.FormatInt(int64(i), 10)
})
// []string{"0", "1", "2"}
Parallel processing: like lo.Times()
, but callback is called in goroutine.
import lop "github.com/samber/lo/parallel"
lop.Times[string](3, func(i int) string {
return strconv.FormatInt(int64(i), 10)
})
// []string{"0", "1", "2"}
You also can control the conurrency limit by optional ParallelOption to limit the maximum number of concurrent iteratee
goroutines running at the same time.
lop.Times(60, iteratee, lop.WithConcurrency(20)) // up to 20 concurrent goroutines running at the same time
Returns a duplicate-free version of an array, in which only the first occurrence of each element is kept. The order of result values is determined by the order they occur in the array.
uniqValues := lo.Uniq[int]([]int{1, 2, 2, 1})
// []int{1, 2}
Returns a duplicate-free version of an array, in which only the first occurrence of each element is kept. The order of result values is determined by the order they occur in the array. It accepts iteratee
which is invoked for each element in array to generate the criterion by which uniqueness is computed.
uniqValues := lo.UniqBy[int, int]([]int{0, 1, 2, 3, 4, 5}, func(i int) int {
return i%3
})
// []int{0, 1, 2}
Returns an object composed of keys generated from the results of running each element of collection through iteratee.
import lo "github.com/samber/lo"
groups := lo.GroupBy[int, int]([]int{0, 1, 2, 3, 4, 5}, func(i int) int {
return i%3
})
// map[int][]int{0: []int{0, 3}, 1: []int{1, 4}, 2: []int{2, 5}}
Parallel processing: like lo.GroupBy()
, but callback is called in goroutine.
import lop "github.com/samber/lo/parallel"
lop.GroupBy[int, int]([]int{0, 1, 2, 3, 4, 5}, func(i int) int {
return i%3
})
// map[int][]int{0: []int{0, 3}, 1: []int{1, 4}, 2: []int{2, 5}}
You also can control the conurrency limit by optional ParallelOption to limit the maximum number of concurrent iteratee
goroutines running at the same time.
lop.GroupBy(list, iteratee, lop.WithConcurrency(20)) // up to 20 concurrent goroutines running at the same time
Returns an array of elements split into groups the length of size. If array can't be split evenly, the final chunk will be the remaining elements.
lo.Chunk[int]([]int{0, 1, 2, 3, 4, 5}, 2)
// [][]int{{0, 1}, {2, 3}, {4, 5}}
lo.Chunk[int]([]int{0, 1, 2, 3, 4, 5, 6}, 2)
// [][]int{{0, 1}, {2, 3}, {4, 5}, {6}}
lo.Chunk[int]([]int{}, 2)
// [][]int{}
lo.Chunk[int]([]int{0}, 2)
// [][]int{{0}}
Returns an array of elements split into groups. The order of grouped values is determined by the order they occur in collection. The grouping is generated from the results of running each element of collection through iteratee.
import lo "github.com/samber/lo"
partitions := lo.PartitionBy[int, string]([]int{-2, -1, 0, 1, 2, 3, 4, 5}, func(x int) string {
if x < 0 {
return "negative"
} else if x%2 == 0 {
return "even"
}
return "odd"
})
// [][]int{{-2, -1}, {0, 2, 4}, {1, 3, 5}}
Parallel processing: like lo.PartitionBy()
, but callback is called in goroutine. Results are returned in the same order.
import lop "github.com/samber/lo/parallel"
partitions := lo.PartitionBy[int, string]([]int{-2, -1, 0, 1, 2, 3, 4, 5}, func(x int) string {
if x < 0 {
return "negative"
} else if x%2 == 0 {
return "even"
}
return "odd"
})
// [][]int{{-2, -1}, {0, 2, 4}, {1, 3, 5}}
You also can control the conurrency limit by optional ParallelOption to limit the maximum number of concurrent iteratee
goroutines running at the same time.
lop.PartitionBy(list, iteratee, lop.WithConcurrency(20)) // up to 20 concurrent goroutines running at the same time
Returns an array a single level deep.
flat := lo.Flatten[int]([][]int{{0, 1}, {2, 3, 4, 5}})
// []int{0, 1, 2, 3, 4, 5}
Returns an array of shuffled values. Uses the Fisher-Yates shuffle algorithm.
randomOrder := lo.Shuffle[int]([]int{0, 1, 2, 3, 4, 5})
// []int{0, 1, 2, 3, 4, 5}
Reverses array so that the first element becomes the last, the second element becomes the second to last, and so on.
reverseOder := lo.Reverse[int]([]int{0, 1, 2, 3, 4, 5})
// []int{5, 4, 3, 2, 1, 0}
Fills elements of array with initial
value.
type foo struct {
bar string
}
func (f foo) Clone() foo {
return foo{f.bar}
}
initializedSlice := lo.Fill[foo]([]foo{foo{"a"}, foo{"a"}}, foo{"b"})
// []foo{foo{"b"}, foo{"b"}}
Builds a slice with N copies of initial value.
type foo struct {
bar string
}
func (f foo) Clone() foo {
return foo{f.bar}
}
slice := lo.Repeat[foo](2, foo{"a"})
// []foo{foo{"a"}, foo{"a"}}
Builds a slice with values returned by N calls of callback.
slice := lo.RepeatBy[int](0, func (i int) int {
return math.Pow(i, 2)
})
// []int{}
slice := lo.RepeatBy[int](5, func (i int) int {
return math.Pow(i, 2)
})
// []int{0, 1, 4, 9, 16}
Transforms a slice or an array of structs to a map based on a pivot callback.
m := lo.KeyBy[int, string]([]string{"a", "aa", "aaa"}, func(str string) int {
return len(str)
})
// map[int]string{1: "a", 2: "aa", 3: "aaa"}
type Character struct {
dir string
code int
}
characters := []Character{
{dir: "left", code: 97},
{dir: "right", code: 100},
}
result := lo.KeyBy[string, Character](characters, func(char Character) string {
return string(rune(char.code))
})
//map[a:{dir:left code:97} d:{dir:right code:100}]
Drops n elements from the beginning of a slice or array.
l := lo.Drop[int]([]int{0, 1, 2, 3, 4, 5}, 2)
// []int{2, 3, 4, 5}
Drops n elements from the end of a slice or array.
l := lo.DropRight[int]([]int{0, 1, 2, 3, 4, 5}, 2)
// []int{0, 1, 2, 3}
Drop elements from the beginning of a slice or array while the predicate returns true.
l := lo.DropWhile[string]([]string{"a", "aa", "aaa", "aa", "aa"}, func(val string) bool {
return len(val) <= 2
})
// []string{"aaa", "aa", "aa"}
Drop elements from the end of a slice or array while the predicate returns true.
l := lo.DropRightWhile[string]([]string{"a", "aa", "aaa", "aa", "aa"}, func(val string) bool {
return len(val) <= 2
})
// []string{"a", "aa", "aaa"}
The opposite of Filter, this method returns the elements of collection that predicate does not return truthy for.
odd := lo.Reject[int]([]int{1, 2, 3, 4}, func(x int, _ int) bool {
return x%2 == 0
})
// []int{1, 3}
Counts the number of elements in the collection that compare equal to value.
count := lo.Count[int]([]int{1, 5, 1}, 1)
// 2
Counts the number of elements in the collection for which predicate is true.
count := lo.CountBy[int]([]int{1, 5, 1}, func(i int) bool {
return i < 4
})
// 2
Returns a copy of a slice from offset
up to length
elements. Like slice[start:start+length]
, but does not panic on overflow.
in := []int{0, 1, 2, 3, 4}
sub := lo.Subset(in, 2, 3)
// []int{2, 3, 4}
sub := lo.Subset(in, -4, 3)
// []int{1, 2, 3}
sub := lo.Subset(in, -2, math.MaxUint)
// []int{3, 4}
Returns a copy of a slice from start
up to, but not including end
. Like slice[start:end]
, but does not panic on overflow.
in := []int{0, 1, 2, 3, 4}
slice := lo.Slice(in, 0, 5)
// []int{0, 1, 2, 3, 4}
slice := lo.Slice(in, 2, 3)
// []int{2}
slice := lo.Slice(in, 2, 6)
// []int{2, 3, 4}
slice := lo.Slice(in, 4, 3)
// []int{}
Returns a copy of the slice with the first n non-overlapping instances of old replaced by new.
in := []int{0, 1, 0, 1, 2, 3, 0}
slice := lo.Replace(in, 0, 42, 1)
// []int{42, 1, 0, 1, 2, 3, 0}
slice := lo.Replace(in, -1, 42, 1)
// []int{0, 1, 0, 1, 2, 3, 0}
slice := lo.Replace(in, 0, 42, 2)
// []int{42, 1, 42, 1, 2, 3, 0}
slice := lo.Replace(in, 0, 42, -1)
// []int{42, 1, 42, 1, 2, 3, 42}
Returns a copy of the slice with all non-overlapping instances of old replaced by new.
in := []int{0, 1, 0, 1, 2, 3, 0}
slice := lo.ReplaceAll(in, 0, 42)
// []int{42, 1, 42, 1, 2, 3, 42}
slice := lo.ReplaceAll(in, -1, 42)
// []int{0, 1, 0, 1, 2, 3, 0}
Returns a slice of all non-zero elements.
in := []string{"", "foo", "", "bar", ""}
slice := lo.Compact[string](in)
// []string{"foo", "bar"}
Creates an array of the map keys.
keys := lo.Keys[string, int](map[string]int{"foo": 1, "bar": 2})
// []string{"bar", "foo"}
Creates an array of the map values.
values := lo.Values[string, int](map[string]int{"foo": 1, "bar": 2})
// []int{1, 2}
Returns same map type filtered by given predicate.
m := lo.PickBy[string, int](map[string]int{"foo": 1, "bar": 2, "baz": 3}, func(key string, value int) bool {
return value%2 == 1
})
// map[string]int{"foo": 1, "baz": 3}
Returns same map type filtered by given keys.
m := lo.PickByKeys[string, int](map[string]int{"foo": 1, "bar": 2, "baz": 3}, []string{"foo", "baz"})
// map[string]int{"foo": 1, "baz": 3}
Returns same map type filtered by given values.
m := lo.PickByValues[string, int](map[string]int{"foo": 1, "bar": 2, "baz": 3}, []int{1, 3})
// map[string]int{"foo": 1, "baz": 3}
Returns same map type filtered by given predicate.
m := lo.OmitBy[string, int](map[string]int{"foo": 1, "bar": 2, "baz": 3}, func(key string, value int) bool {
return value%2 == 1
})
// map[string]int{"bar": 2}
Returns same map type filtered by given keys.
m := lo.OmitByKeys[string, int](map[string]int{"foo": 1, "bar": 2, "baz": 3}, []string{"foo", "baz"})
// map[string]int{"bar": 2}
Returns same map type filtered by given values.
m := lo.OmitByValues[string, int](map[string]int{"foo": 1, "bar": 2, "baz": 3}, []int{1, 3})
// map[string]int{"bar": 2}
Transforms a map into array of key/value pairs.
entries := lo.Entries[string, int](map[string]int{"foo": 1, "bar": 2})
// []lo.Entry[string, int]{
// {
// Key: "foo",
// Value: 1,
// },
// {
// Key: "bar",
// Value: 2,
// },
// }
Transforms an array of key/value pairs into a map.
m := lo.FromEntries[string, int]([]lo.Entry[string, int]{
{
Key: "foo",
Value: 1,
},
{
Key: "bar",
Value: 2,
},
})
// map[string]int{"foo": 1, "bar": 2}
Creates a map composed of the inverted keys and values. If map contains duplicate values, subsequent values overwrite property assignments of previous values.
m1 := lo.Invert[string, int]([map[string]int{"a": 1, "b": 2})
// map[int]string{1: "a", 2: "b"}
m2 := lo.Invert[string, int]([map[string]int{"a": 1, "b": 2, "c": 1})
// map[int]string{1: "c", 2: "b"}
Merges multiple maps from left to right.
mergedMaps := lo.Assign[string, int](
map[string]int{"a": 1, "b": 2},
map[string]int{"b": 3, "c": 4},
)
// map[string]int{"a": 1, "b": 3, "c": 4}
Manipulates a map keys and transforms it to a map of another type.
m2 := lo.MapKeys[int, int, string](map[int]int{1: 1, 2: 2, 3: 3, 4: 4}, func(_ int, v int) string {
return strconv.FormatInt(int64(v), 10)
})
// map[string]int{"1": 1, "2": 2, "3": 3, "4": 4}
Manipulates a map values and transforms it to a map of another type.
m1 := map[int]int64{1: 1, 2: 2, 3: 3}
m2 := lo.MapValues[int, int64, string](m1, func(x int64, _ int) string {
return strconv.FormatInt(x, 10)
})
// map[int]string{1: "1", 2: "2", 3: "3"}
Creates an array of numbers (positive and/or negative) progressing from start up to, but not including end.
result := Range(4)
// [0, 1, 2, 3]
result := Range(-4);
// [0, -1, -2, -3]
result := RangeFrom(1, 5);
// [1, 2, 3, 4]
result := RangeFrom[float64](1.0, 5);
// [1.0, 2.0, 3.0, 4.0]
result := RangeWithSteps(0, 20, 5);
// [0, 5, 10, 15]
result := RangeWithSteps[float32](-1.0, -4.0, -1.0);
// [-1.0, -2.0, -3.0]
result := RangeWithSteps(1, 4, -1);
// []
result := Range(0);
// []
Clamps number within the inclusive lower and upper bounds.
r1 := lo.Clamp(0, -10, 10)
// 0
r2 := lo.Clamp(-42, -10, 10)
// -10
r3 := lo.Clamp(42, -10, 10)
// 10
Summarizes the values in a collection using the given return value from the iteration function. If collection is empty 0 is returned.
strings := []string{"foo", "bar"}
sum := lo.SumBy(strings, func(item string) int {
return len(item)
})
// 6
Return part of a string.
sub := lo.Substring("hello", 2, 3)
// "llo"
sub := lo.Substring("hello", -4, 3)
// "ell"
sub := lo.Substring("hello", -2, math.MaxUint)
// "lo"
An alias to utf8.RuneCountInString which returns the number of runes in string.
sub := lo.RuneLength("hellΓ΄")
// 5
sub := len("hellΓ΄")
// 6
Creates a tuple from a list of values.
tuple1 := lo.T2[string, int]("x", 1)
// Tuple2[string, int]{A: "x", B: 1}
func example() (string, int) { return "y", 2 }
tuple2 := lo.T2[string, int](example())
// Tuple2[string, int]{A: "y", B: 2}
Returns values contained in tuple.
r1, r2 := lo.Unpack2[string, int](lo.Tuple2[string, int]{"a", 1})
// "a", 1
Zip creates a slice of grouped elements, the first of which contains the first elements of the given arrays, the second of which contains the second elements of the given arrays, and so on.
When collections have different size, the Tuple attributes are filled with zero value.
tuples := lo.Zip2[string, int]([]string{"a", "b"}, []int{1, 2})
// []Tuple2[string, int]{{A: "a", B: 1}, {A: "b", B: 2}}
Unzip accepts an array of grouped elements and creates an array regrouping the elements to their pre-zip configuration.
a, b := lo.Unzip2[string, int]([]Tuple2[string, int]{{A: "a", B: 1}, {A: "b", B: 2}})
// []string{"a", "b"}
// []int{1, 2}
Returns true if an element is present in a collection.
present := lo.Contains[int]([]int{0, 1, 2, 3, 4, 5}, 5)
// true
Returns true if the predicate function returns true
.
present := lo.ContainsBy[int]([]int{0, 1, 2, 3, 4, 5}, func(x int) bool {
return x == 3
})
// true
Returns true if all elements of a subset are contained into a collection or if the subset is empty.
ok := lo.Every[int]([]int{0, 1, 2, 3, 4, 5}, []int{0, 2})
// true
ok := lo.Every[int]([]int{0, 1, 2, 3, 4, 5}, []int{0, 6})
// false
Returns true if the predicate returns true for all of the elements in the collection or if the collection is empty.
b := EveryBy[int]([]int{1, 2, 3, 4}, func(x int) bool {
return x < 5
})
// true
Returns true if at least 1 element of a subset is contained into a collection. If the subset is empty Some returns false.
ok := lo.Some[int]([]int{0, 1, 2, 3, 4, 5}, []int{0, 2})
// true
ok := lo.Some[int]([]int{0, 1, 2, 3, 4, 5}, []int{-1, 6})
// false
Returns true if the predicate returns true for any of the elements in the collection. If the collection is empty SomeBy returns false.
b := SomeBy[int]([]int{1, 2, 3, 4}, func(x int) bool {
return x < 3
})
// true
Returns true if no element of a subset are contained into a collection or if the subset is empty.
b := None[int]([]int{0, 1, 2, 3, 4, 5}, []int{0, 2})
// false
b := None[int]([]int{0, 1, 2, 3, 4, 5}, []int{-1, 6})
// true
Returns true if the predicate returns true for none of the elements in the collection or if the collection is empty.
b := NoneBy[int]([]int{1, 2, 3, 4}, func(x int) bool {
return x < 0
})
// true
Returns the intersection between two collections.
result1 := lo.Intersect[int]([]int{0, 1, 2, 3, 4, 5}, []int{0, 2})
// []int{0, 2}
result2 := lo.Intersect[int]([]int{0, 1, 2, 3, 4, 5}, []int{0, 6}
// []int{0}
result3 := lo.Intersect[int]([]int{0, 1, 2, 3, 4, 5}, []int{-1, 6})
// []int{}
Returns the difference between two collections.
- The first value is the collection of element absent of list2.
- The second value is the collection of element absent of list1.
left, right := lo.Difference[int]([]int{0, 1, 2, 3, 4, 5}, []int{0, 2, 6})
// []int{1, 3, 4, 5}, []int{6}
left, right := lo.Difference[int]([]int{0, 1, 2, 3, 4, 5}, []int{0, 1, 2, 3, 4, 5})
// []int{}, []int{}
Returns all distinct elements from both collections. Result will not change the order of elements relatively.
union := lo.Union[int]([]int{0, 1, 2, 3, 4, 5}, []int{0, 2, 10})
// []int{0, 1, 2, 3, 4, 5, 10}
Returns slice excluding all given values.
subset := lo.Without[int]([]int{0, 2, 10}, 2)
// []int{0, 10}
subset := lo.Without[int]([]int{0, 2, 10}, 0, 1, 2, 3, 4, 5)
// []int{10}
Returns slice excluding empty values.
subset := lo.WithoutEmpty[int]([]int{0, 2, 10})
// []int{2, 10}
Returns the index at which the first occurrence of a value is found in an array or return -1 if the value cannot be found.
found := lo.IndexOf[int]([]int{0, 1, 2, 1, 2, 3}, 2)
// 2
notFound := lo.IndexOf[int]([]int{0, 1, 2, 1, 2, 3}, 6)
// -1
Returns the index at which the last occurrence of a value is found in an array or return -1 if the value cannot be found.
found := lo.LastIndexOf[int]([]int{0, 1, 2, 1, 2, 3}, 2)
// 4
notFound := lo.LastIndexOf[int]([]int{0, 1, 2, 1, 2, 3}, 6)
// -1
Search an element in a slice based on a predicate. It returns element and true if element was found.
str, ok := lo.Find[string]([]string{"a", "b", "c", "d"}, func(i string) bool {
return i == "b"
})
// "b", true
str, ok := lo.Find[string]([]string{"foobar"}, func(i string) bool {
return i == "b"
})
// "", false
FindIndexOf searches an element in a slice based on a predicate and returns the index and true. It returns -1 and false if the element is not found.
str, index, ok := lo.FindIndexOf[string]([]string{"a", "b", "a", "b"}, func(i string) bool {
return i == "b"
})
// "b", 1, true
str, index, ok := lo.FindIndexOf[string]([]string{"foobar"}, func(i string) bool {
return i == "b"
})
// "", -1, false
FindLastIndexOf searches an element in a slice based on a predicate and returns the index and true. It returns -1 and false if the element is not found.
str, index, ok := lo.FindLastIndexOf[string]([]string{"a", "b", "a", "b"}, func(i string) bool {
return i == "b"
})
// "b", 4, true
str, index, ok := lo.FindLastIndexOf[string]([]string{"foobar"}, func(i string) bool {
return i == "b"
})
// "", -1, false
Returns the key of the first value matching.
result1, ok1 := lo.FindKey(map[string]int{"foo": 1, "bar": 2, "baz": 3}, 2)
// "bar", true
result2, ok2 := lo.FindKey(map[string]int{"foo": 1, "bar": 2, "baz": 3}, 42)
// "", false
type test struct {
foobar string
}
result3, ok3 := lo.FindKey(map[string]test{"foo": test{"foo"}, "bar": test{"bar"}, "baz": test{"baz"}}, test{"foo"})
// "foo", true
Returns the key of the first element predicate returns truthy for.
result1, ok1 := lo.FindKeyBy(map[string]int{"foo": 1, "bar": 2, "baz": 3}, func(k string, v int) bool {
return k == "foo"
})
// "foo", true
result2, ok2 := lo.FindKeyBy(map[string]int{"foo": 1, "bar": 2, "baz": 3}, func(k string, v int) bool {
return false
})
// "", false
Returns a slice with all the unique elements of the collection. The order of result values is determined by the order they occur in the array.
uniqueValues := lo.FindUniques[int]([]int{1, 2, 2, 1, 2, 3})
// []int{3}
Returns a slice with all the unique elements of the collection. The order of result values is determined by the order they occur in the array. It accepts iteratee
which is invoked for each element in array to generate the criterion by which uniqueness is computed.
uniqueValues := lo.FindUniquesBy[int, int]([]int{3, 4, 5, 6, 7}, func(i int) int {
return i%3
})
// []int{5}
Returns a slice with the first occurence of each duplicated elements of the collection. The order of result values is determined by the order they occur in the array.
duplicatedValues := lo.FindDuplicates[int]([]int{1, 2, 2, 1, 2, 3})
// []int{1, 2}
Returns a slice with the first occurence of each duplicated elements of the collection. The order of result values is determined by the order they occur in the array. It accepts iteratee
which is invoked for each element in array to generate the criterion by which uniqueness is computed.
duplicatedValues := lo.FindDuplicatesBy[int, int]([]int{3, 4, 5, 6, 7}, func(i int) int {
return i%3
})
// []int{3, 4}
Search the minimum value of a collection.
min := lo.Min[int]([]int{1, 2, 3})
// 1
min := lo.Min[int]([]int{})
// 0
Search the minimum value of a collection using the given comparison function. If several values of the collection are equal to the smallest value, returns the first such value.
min := lo.MinBy[string]([]string{"s1", "string2", "s3"}, func(item string, min string) bool {
return len(item) < len(min)
})
// "s1"
min := lo.MinBy[string]([]string{}, func(item string, min string) bool {
return len(item) < len(min)
})
// ""
Search the maximum value of a collection.
max := lo.Max[int]([]int{1, 2, 3})
// 3
max := lo.Max[int]([]int{})
// 0
Search the maximum value of a collection using the given comparison function. If several values of the collection are equal to the greatest value, returns the first such value.
max := lo.MaxBy[string]([]string{"string1", "s2", "string3"}, func(item string, max string) bool {
return len(item) > len(max)
})
// "string1"
max := lo.MaxBy[string]([]string{}, func(item string, max string) bool {
return len(item) > len(max)
})
// ""
Returns the last element of a collection or error if empty.
last, err := lo.Last[int]([]int{1, 2, 3})
// 3
Returns the element at index nth
of collection. If nth
is negative, the nth element from the end is returned. An error is returned when nth is out of slice bounds.
nth, err := lo.Nth[int]([]int{0, 1, 2, 3}, 2)
// 2
nth, err := lo.Nth[int]([]int{0, 1, 2, 3}, -2)
// 2
Returns a random item from collection.
lo.Sample[string]([]string{"a", "b", "c"})
// a random string from []string{"a", "b", "c"}
lo.Sample[string]([]string{})
// ""
Returns N random unique items from collection.
lo.Samples[string]([]string{"a", "b", "c"}, 3)
// []string{"a", "b", "c"} in random order
A 1 line if/else statement.
result := lo.Ternary[string](true, "a", "b")
// "a"
result := lo.Ternary[string](false, "a", "b")
// "b"
result := lo.If[int](true, 1).
ElseIf(false, 2).
Else(3)
// 1
result := lo.If[int](false, 1).
ElseIf(true, 2).
Else(3)
// 2
result := lo.If[int](false, 1).
ElseIf(false, 2).
Else(3)
// 3
Using callbacks:
result := lo.IfF[int](true, func () int {
return 1
}).
ElseIfF(false, func () int {
return 2
}).
ElseF(func () int {
return 3
})
// 1
Mixed:
result := lo.IfF[int](true, func () int {
return 1
}).
Else(42)
// 1
result := lo.Switch[int, string](1).
Case(1, "1").
Case(2, "2").
Default("3")
// "1"
result := lo.Switch[int, string](2).
Case(1, "1").
Case(2, "2").
Default("3")
// "2"
result := lo.Switch[int, string](42).
Case(1, "1").
Case(2, "2").
Default("3")
// "3"
Using callbacks:
result := lo.Switch[int, string](1).
CaseF(1, func() string {
return "1"
}).
CaseF(2, func() string {
return "2"
}).
DefaultF(func() string {
return "3"
})
// "1"
Mixed:
result := lo.Switch[int, string](1).
CaseF(1, func() string {
return "1"
}).
Default("42")
// "1"
Returns a pointer copy of value.
ptr := lo.ToPtr[string]("hello world")
// *string{"hello world"}
Returns the pointer value or empty.
str := "hello world"
value := lo.FromPtr[string](&str)
// "hello world"
value := lo.FromPtr[string](nil)
// ""
Returns a slice of pointer copy of value.
ptr := lo.ToSlicePtr[string]([]string{"hello", "world"})
// []*string{"hello", "world"}
Returns a slice with all elements mapped to any
type.
elements := lo.ToAnySlice[int]([]int{1, 5, 1})
// []any{1, 5, 1}
Returns an any
slice with all elements mapped to a type. Returns false in case of type conversion failure.
elements, ok := lo.FromAnySlice[string]([]any{"foobar", 42})
// []string{}, false
elements, ok := lo.FromAnySlice[string]([]any{"foobar", "42"})
// []string{"foobar", "42"}, true
Returns an empty value.
lo.Empty[int]()
// 0
lo.Empty[string]()
// ""
lo.Empty[bool]()
// false
Returns true if argument is a zero value.
lo.IsEmpty[int](0)
// true
lo.IsEmpty[int](42)
// false
lo.IsEmpty[string]("")
// true
lo.IsEmpty[bool]("foobar")
// false
type test struct {
foobar string
}
lo.IsEmpty[test](test{foobar: ""})
// true
lo.IsEmpty[test](test{foobar: "foobar"})
// false
Returns true if argument is a zero value.
lo.IsNotEmpty[int](0)
// false
lo.IsNotEmpty[int](42)
// true
lo.IsNotEmpty[string]("")
// false
lo.IsNotEmpty[bool]("foobar")
// true
type test struct {
foobar string
}
lo.IsNotEmpty[test](test{foobar: ""})
// false
lo.IsNotEmpty[test](test{foobar: "foobar"})
// true
Returns the first non-empty arguments. Arguments must be comparable.
result, ok := lo.Coalesce(0, 1, 2, 3)
// 1 true
result, ok := lo.Coalesce("")
// "" false
var nilStr *string
str := "foobar"
result, ok := lo.Coalesce[*string](nil, nilStr, &str)
// &"foobar" true
Returns new function that, when called, has its first argument set to the provided value.
add := func(x, y int) int { return x + y }
f := lo.Partial(add, 5)
f(10)
// 15
f(42)
// 47
Invokes a function N times until it returns valid output. Returning either the caught error or nil. When first argument is less than 1
, the function runs until a successful response is returned.
iter, err := lo.Attempt(42, func(i int) error {
if i == 5 {
return nil
}
return fmt.Errorf("failed")
})
// 6
// nil
iter, err := lo.Attempt(2, func(i int) error {
if i == 5 {
return nil
}
return fmt.Errorf("failed")
})
// 2
// error "failed"
iter, err := lo.Attempt(0, func(i int) error {
if i < 42 {
return fmt.Errorf("failed")
}
return nil
})
// 43
// nil
For more advanced retry strategies (delay, exponential backoff...), please take a look on cenkalti/backoff.
Invokes a function N times until it returns valid output, with a pause between each call. Returning either the caught error or nil.
When first argument is less than 1
, the function runs until a successful response is returned.
iter, duration, err := lo.AttemptWithDelay(5, 2*time.Second, func(i int, duration time.Duration) error {
if i == 2 {
return nil
}
return fmt.Errorf("failed")
})
// 3
// ~ 4 seconds
// nil
For more advanced retry strategies (delay, exponential backoff...), please take a look on cenkalti/backoff.
NewDebounce
creates a debounced instance that delays invoking functions given until after wait milliseconds have elapsed, until cancel
is called.
f := func() {
println("Called once after 100ms when debounce stopped invoking!")
}
debounce, cancel := lo.NewDebounce(100 * time.Millisecond, f)
for j := 0; j < 10; j++ {
debounce()
}
time.Sleep(1 * time.Second)
cancel()
Wraps the underlying callback in a mutex. It receives an optional mutex.
s := lo.Synchronize()
for i := 0; i < 10; i++ {
go s.Do(func () {
println("will be called sequentially")
})
}
It is equivalent to:
mu := sync.Mutex{}
func foobar() {
mu.Lock()
defer mu.Unlock()
// ...
}
Executes a function in a goroutine and returns the result in a channel.
ch := lo.Async(func() error { time.Sleep(10 * time.Second); return nil })
// chan error (nil)
Executes a function in a goroutine and returns the result in a channel. For function with multiple return values, the results will be returned as a tuple inside the channel. For function without return, struct{} will be returned in the channel.
ch := lo.Async0(func() { time.Sleep(10 * time.Second) })
// chan struct{}
ch := lo.Async1(func() int {
time.Sleep(10 * time.Second);
return 42
})
// chan int (42)
ch := lo.Async2(func() (int, string) {
time.Sleep(10 * time.Second);
return 42, "Hello"
})
// chan lo.Tuple2[int, string] ({42, "Hello"})
Wraps a function call to panics if second argument is error
or false
, returns the value otherwise.
val := lo.Must(time.Parse("2006-01-02", "2022-01-15"))
// 2022-01-15
val := lo.Must(time.Parse("2006-01-02", "bad-value"))
// panics
Must* has the same behavior than Must, but returns multiple values.
func example0() (error)
func example1() (int, error)
func example2() (int, string, error)
func example3() (int, string, time.Date, error)
func example4() (int, string, time.Date, bool, error)
func example5() (int, string, time.Date, bool, float64, error)
func example6() (int, string, time.Date, bool, float64, byte, error)
lo.Must0(example0())
val1 := lo.Must1(example1()) // alias to Must
val1, val2 := lo.Must2(example2())
val1, val2, val3 := lo.Must3(example3())
val1, val2, val3, val4 := lo.Must4(example4())
val1, val2, val3, val4, val5 := lo.Must5(example5())
val1, val2, val3, val4, val5, val6 := lo.Must6(example6())
You can wrap functions like func (...) (..., ok bool)
.
// math.Signbit(float64) bool
lo.Must0(math.Signbit(v))
// bytes.Cut([]byte,[]byte) ([]byte, []byte, bool)
before, after := lo.Must2(bytes.Cut(s, sep))
You can give context to the panic message by adding some printf-like arguments.
val := lo.Must(lo.Find(myString, func(i string) bool {
return i == requiredChar
}), "'%s' must always contain '%s'", myString, requiredChar)
// MustX
lo.Must0(example0(), "'%s' must always contain '%s'", myString, requiredChar)
val1 := lo.Must1(example1(), "'%s' must always contain '%s'", myString, requiredChar)
val1, val2 := lo.Must2(example2(), "'%s' must always contain '%s'", myString, requiredChar)
...
Calls the function and return false in case of error and on panic.
ok := lo.Try(func() error {
panic("error")
return nil
})
// false
ok := lo.Try(func() error {
return nil
})
// true
ok := lo.Try(func() error {
return fmt.Errorf("error")
})
// false
The same behavior than Try
, but callback returns 2 variables.
ok := lo.Try2(func() (string, error) {
panic("error")
return "", nil
})
// false
The same behavior than Try
, but also returns value passed to panic.
err, ok := lo.TryWithErrorValue(func() error {
panic("error")
return nil
})
// "error", false
The same behavior than Try
, but calls the catch function in case of error.
caught := false
ok := lo.TryCatch(func() error {
panic("error")
return nil
}, func() {
caught = true
})
// false
// caught == true
The same behavior than TryWithErrorValue
, but calls the catch function in case of error.
caught := false
ok := lo.TryCatchWithErrorValue(func() error {
panic("error")
return nil
}, func(val any) {
caught = val == "error"
})
// false
// caught == true
We executed a simple benchmark with the a dead-simple lo.Map
loop:
See the full implementation here.
_ = lo.Map[int64](arr, func(x int64, i int) string {
return strconv.FormatInt(x, 10)
})
Result:
Here is a comparison between lo.Map
, lop.Map
, go-funk
library and a simple Go for
loop.
$ go test -benchmem -bench ./...
goos: linux
goarch: amd64
pkg: github.com/samber/lo
cpu: Intel(R) Core(TM) i5-7267U CPU @ 3.10GHz
cpu: Intel(R) Core(TM) i7 CPU 920 @ 2.67GHz
BenchmarkMap/lo.Map-8 8 132728237 ns/op 39998945 B/op 1000002 allocs/op
BenchmarkMap/lop.Map-8 2 503947830 ns/op 119999956 B/op 3000007 allocs/op
BenchmarkMap/reflect-8 2 826400560 ns/op 170326512 B/op 4000042 allocs/op
BenchmarkMap/for-8 9 126252954 ns/op 39998674 B/op 1000001 allocs/op
PASS
ok github.com/samber/lo 6.657s
lo.Map
is way faster (x7) thango-funk
, a reflection-based Map implementation.lo.Map
have the same allocation profile thanfor
.lo.Map
is 4% slower thanfor
.lop.Map
is slower thanlo.Map
because it implies more memory allocation and locks.lop.Map
will be useful for long-running callbacks, such as i/o bound processing.for
beats other implementations for memory and CPU.
- Ping me on twitter @samuelberthe (DMs, mentions, whatever :))
- Fork the project
- Fix open issues or request new features
Don't hesitate ;)
make go1.18beta1
If your OS currently not default to Go 1.18, replace BIN=go
by BIN=go1.18beta1
in the Makefile.
docker-compose run --rm dev
# Install some dev dependencies
make tools
# Run tests
make test
# or
make watch-test
- Samuel Berthe
Give a βοΈ if this project helped you!
Copyright Β© 2022 Samuel Berthe.
This project is MIT licensed.