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More uses of Object.groupBy — countBy, partition, simpler version of chunk #397

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More uses of Object.groupBy — countBy, partition, simpler version of chunk #397

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117 changes: 113 additions & 4 deletions README.md
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Original file line number Diff line number Diff line change
Expand Up @@ -111,6 +111,7 @@ For more information, see [Configuring the ESLint Plugin](configuring.md)
> objects can easily be converted to an array by use of the
> [spread operator](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Spread_syntax).

1. [_.countBy](#_countBy)
1. [_.each](#_each)
1. [_.every](#_every)
1. [_.filter](#_filter)
Expand All @@ -120,6 +121,7 @@ For more information, see [Configuring the ESLint Plugin](configuring.md)
1. [_.map](#_map)
1. [_.minBy and _.maxBy](#_minby-and-_maxby)
1. [_.orderBy](#_sortby-and-_orderby)
1. [_.partition](#_partition)
1. [_.pluck](#_pluck)
1. [_.range](#_range)
1. [_.reduce](#_reduce)
Expand Down Expand Up @@ -204,6 +206,7 @@ For more information, see [Configuring the ESLint Plugin](configuring.md)
### _.chunk

Creates an array of elements split into groups the length of size.

```js
// Underscore/Lodash
_.chunk(['a', 'b', 'c', 'd'], 2);
Expand All @@ -212,24 +215,41 @@ _.chunk(['a', 'b', 'c', 'd'], 2);
_.chunk(['a', 'b', 'c', 'd'], 3);
// => [['a', 'b', 'c'], ['d']]


// Native
function chunk(input, size) {
return Object.values(
Object.groupBy(input, (_, i) => Math.floor(i / size))
);
}

chunk(['a', 'b', 'c', 'd'], 2);
// => [['a', 'b'], ['c', 'd']]

chunk(['a', 'b', 'c', 'd'], 3);
// => [['a', 'b', 'c'], ['d']]

const chunk = (input, size) => {
// Native #2 (if `Object.groupBy` unavailable)
const chunkReduce = (input, size) => {
return input.reduce((arr, item, idx) => {
return idx % size === 0
? [...arr, [item]]
: [...arr.slice(0, -1), [...arr.slice(-1)[0], item]];
}, []);
};

chunk(['a', 'b', 'c', 'd'], 2);
chunkReduce(['a', 'b', 'c', 'd'], 2);
// => [['a', 'b'], ['c', 'd']]

chunk(['a', 'b', 'c', 'd'], 3);
chunkReduce(['a', 'b', 'c', 'd'], 3);
// => [['a', 'b', 'c'], ['d']]
```

#### Browser Support for `Object.groupBy()`

![Chrome][chrome-image] | ![Edge][edge-image] | ![Firefox][firefox-image] | ![IE][ie-image] | ![Opera][opera-image] | ![Safari][safari-image]
:-: | :-: | :-: | :-: | :-: | :-: |
117.0 ✔ | 117.0 ✔ | 119.0 ✔ | ✖ | 103.0 ✔ | 16.4 ✔ |

#### Browser Support for Spread in array literals

![Chrome][chrome-image] | ![Edge][edge-image] | ![Firefox][firefox-image] | ![IE][ie-image] | ![Opera][opera-image] | ![Safari][safari-image]
Expand Down Expand Up @@ -1198,6 +1218,40 @@ Creates an array of unique values, taking an `iteratee` to compute uniqueness wi
> and will not work with objects. If this functionality is needed and no object method is provided,
> then Lodash/Underscore is the better option.

### _.countBy

```js
// Underscore/Lodash
_.countBy([6.1, 4.2, 6.3], Math.floor);
// => { '4': 1, '6': 2 }

// The `_.property` iteratee shorthand.
_.countBy(['one', 'two', 'three'], 'length');
// => { '3': 2, '5': 1 }

// Native
function countBy(input, fn) {
return Object.fromEntries(
Object.entries(Object.groupBy(input, fn)).map(([k, v]) => [k, v.length])
);
}

countBy([6.1, 4.2, 6.3], Math.floor);
// => { '4': 1, '6': 2 }

// Use explicit callback instead of property name
countBy(['one', 'two', 'three'], (x) => x.length);
// => { '3': 2, '5': 1 }
```

#### Browser Support for `Object.groupBy()`

![Chrome][chrome-image] | ![Edge][edge-image] | ![Firefox][firefox-image] | ![IE][ie-image] | ![Opera][opera-image] | ![Safari][safari-image]
:-: | :-: | :-: | :-: | :-: | :-: |
117.0 ✔ | 117.0 ✔ | 119.0 ✔ | ✖ | 103.0 ✔ | 16.4 ✔ |

**[⬆ back to top](#quick-links)**

### _.each

Iterates over a list of elements, yielding each in turn to an iteratee function.
Expand Down Expand Up @@ -1545,6 +1599,61 @@ Extract a functor and use es2015 for better code

**[⬆ back to top](#quick-links)**

### _.partition

```js
// Underscore/Lodash
var users = [
{ 'user': 'barney', 'age': 36, 'active': false },
{ 'user': 'fred', 'age': 40, 'active': true },
{ 'user': 'pebbles', 'age': 1, 'active': false }
];

_.partition(users, function (o) { return o.active; });
// => objects for [['fred'], ['barney', 'pebbles']]

// The `_.matches` iteratee shorthand.
_.partition(users, { 'age': 1, 'active': false });
// => objects for [['pebbles'], ['barney', 'fred']]

// The `_.matchesProperty` iteratee shorthand.
_.partition(users, ['active', false]);
// => objects for [['barney', 'pebbles'], ['fred']]

// The `_.property` iteratee shorthand.
_.partition(users, 'active');
// => objects for [['fred'], ['barney', 'pebbles']]

// Native
function partition(input, fn) {
const results = Object.groupBy(input, (x) => Boolean(fn(x)))
return [results.true ?? [], results.false ?? []]
}

partition(users, (x) => x.active);
// => objects for [['fred'], ['barney', 'pebbles']]

// Use explicit callback instead of object partial
partition(users, (x) => x.age === 1 && !x.active);
// => objects for [['pebbles'], ['barney', 'fred']]

// Use explicit callback instead of [key, val] tuple
partition(users, (x) => !x.active);
// => objects for [['barney', 'pebbles'], ['fred']]

// Use explicit callback instead of property key
partition(users, (x) => x.active);
// => objects for [['fred'], ['barney', 'pebbles']]
```

#### Browser Support for `Object.groupBy()`

![Chrome][chrome-image] | ![Edge][edge-image] | ![Firefox][firefox-image] | ![IE][ie-image] | ![Opera][opera-image] | ![Safari][safari-image]
:-: | :-: | :-: | :-: | :-: | :-: |
117.0 ✔ | 117.0 ✔ | 119.0 ✔ | ✖ | 103.0 ✔ | 16.4 ✔ |

**[⬆ back to top](#quick-links)**

### _.pluck

`array.map` or `_.map` can also be used to replace `_.pluck`.
Expand Down
74 changes: 74 additions & 0 deletions tests/unit/all.js
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Original file line number Diff line number Diff line change
Expand Up @@ -136,6 +136,25 @@ describe('code snippet example', () => {
)
})
})
describe('chunk (Object.groupBy version)', () => {
function chunk(input, size) {
return Object.values(
Object.groupBy(input, (_, i) => Math.floor(i / size))
);
}
it("_.chunk(['a', 'b', 'c', 'd'], 2);", () => {
assert.deepEqual(
_.chunk(['a', 'b', 'c', 'd'], 2),
chunk(['a', 'b', 'c', 'd'], 2)
);
})
it("_.chunk(['a', 'b', 'c', 'd'], 3);", () => {
assert.deepEqual(
_.chunk(['a', 'b', 'c', 'd'], 3),
chunk(['a', 'b', 'c', 'd'], 3)
);
})
})
describe('times', () => {
const times = (n, fn = (_, x) => x) => {
return Array.from(Array(n), fn)
Expand Down Expand Up @@ -1098,4 +1117,59 @@ describe('code snippet example', () => {
assert.deepEqual(_.head([]), [].at(0));
});
})

describe('countBy', () => {
function countBy(input, fn) {
return Object.fromEntries(
Object.entries(Object.groupBy(input, fn)).map(([k, v]) => [k, v.length])
);
}

it('_.countBy([6.1, 4.2, 6.3], Math.floor)', () => {
const lo = _.countBy([6.1, 4.2, 6.3], Math.floor);
const native = countBy([6.1, 4.2, 6.3], Math.floor);
assert.deepEqual(lo, native);
});
it("_.countBy(['one', 'two', 'three'], 'length')", () => {
const lo = _.countBy(['one', 'two', 'three'], 'length');
const native = countBy(['one', 'two', 'three'], (x) => x.length);
assert.deepEqual(lo, native);
});
});

describe('partition', () => {
// Underscore/Lodash
var users = [
{ 'user': 'barney', 'age': 36, 'active': false },
{ 'user': 'fred', 'age': 40, 'active': true },
{ 'user': 'pebbles', 'age': 1, 'active': false }
];

function partition(input, fn) {
const results = Object.groupBy(input, (x) => Boolean(fn(x)))
return [results.true ?? [], results.false ?? []]
}

it("_.partition(users, function (o) { return o.active; });", () => {
const lo = _.partition(users, function (o) { return o.active; });
const native = partition(users, (x) => x.active);

assert.deepEqual(lo, native);
});
it("_.partition(users, { 'age': 1, 'active': false });", () => {
const lo = _.partition(users, { 'age': 1, 'active': false });
const native = partition(users, (x) => x.age === 1 && !x.active);
assert.deepEqual(lo, native);
});
it("_.partition(users, ['active', false]);", () => {
const lo = _.partition(users, ['active', false]);
const native = partition(users, (x) => !x.active);
assert.deepEqual(lo, native);
});
it("_.partition(users, 'active');", () => {
const lo = _.partition(users, 'active');
const native = partition(users, (x) => x.active);
assert.deepEqual(lo, native);
});
})
});