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expr_reduce.go
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/
expr_reduce.go
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package rel
import (
"fmt"
"github.com/arr-ai/wbnf/parser"
"github.com/pkg/errors"
)
// ReduceExpr represents a range of operators.
type ReduceExpr struct {
ExprScanner
a Expr
f *Function
format string
init func(s Set) (interface{}, error)
reduce func(acc interface{}, v Value) (interface{}, error)
output func(acc interface{}) (Value, error)
}
// NewReduceExpr evaluates a reduce f, given a set lhs.
func NewReduceExpr(scanner parser.Scanner,
a Expr,
f *Function,
format string,
init func(s Set) (interface{}, error),
reduce func(acc interface{}, v Value) (interface{}, error),
output func(acc interface{}) (Value, error),
) Expr {
return &ReduceExpr{ExprScanner{scanner}, a, f, format, init, reduce, output}
}
// NewSumExpr evaluates to the sum of expr over all elements in a.
func NewSumExpr(scanner parser.Scanner, a, b Expr) Expr {
return NewReduceExpr(
scanner, a, ExprAsFunction(b), "%s sum ???",
func(s Set) (interface{}, error) {
return 0.0, nil
},
func(acc interface{}, v Value) (interface{}, error) {
switch v := v.(type) {
case Number:
return acc.(float64) + v.Float64(), nil
}
return nil, errors.Errorf("Non-numeric value used in sum")
},
func(acc interface{}) (Value, error) {
return NewNumber(acc.(float64)), nil
},
)
}
// NewMaxExpr evaluates to the max of expr over all elements in a.
func NewMaxExpr(scanner parser.Scanner, a, b Expr) Expr {
return NewReduceExpr(
scanner, a, ExprAsFunction(b), "%s max ???",
func(s Set) (interface{}, error) {
if s.IsTrue() {
return nil, nil
}
return nil, errors.Errorf("Empty set has no max")
},
func(acc interface{}, v Value) (interface{}, error) {
if acc == nil || acc.(Value).Less(v) {
return v, nil
}
return acc, nil
},
func(acc interface{}) (Value, error) {
if acc != nil {
return acc.(Value), nil
}
return nil, errors.Errorf("Empty input to max")
},
)
}
// NewMeanExpr evaluates to the mean of expr over all elements in a.
func NewMeanExpr(scanner parser.Scanner, a, b Expr) Expr {
type Agg struct {
sum float64
n int
}
return NewReduceExpr(
scanner, a, ExprAsFunction(b), "%s mean ???",
func(s Set) (interface{}, error) {
if n := s.Count(); n > 0 {
return Agg{n: n}, nil
}
return nil, errors.Errorf("Empty set has no mean")
},
func(acc interface{}, v Value) (interface{}, error) {
agg := acc.(Agg)
if v, ok := v.(Number); ok {
return Agg{sum: agg.sum + v.Float64(), n: agg.n}, nil
}
return nil, errors.Errorf("Non-numeric value used in mean")
},
func(acc interface{}) (Value, error) {
agg := acc.(Agg)
if agg.n != 0 {
return NewNumber(agg.sum / float64(agg.n)), nil
}
return nil, errors.Errorf("Non-numeric value used in mean")
},
)
}
// NewMinExpr evaluates to the min of expr over all elements in a.
func NewMinExpr(scanner parser.Scanner, a, b Expr) Expr {
return NewReduceExpr(
scanner, a, ExprAsFunction(b), "%s min ???",
func(s Set) (interface{}, error) {
if s.IsTrue() {
return nil, nil
}
return nil, errors.Errorf("Empty set has no min")
},
func(acc interface{}, v Value) (interface{}, error) {
if acc == nil || v.Less(acc.(Value)) {
return v, nil
}
return acc, nil
},
func(acc interface{}) (Value, error) {
if acc != nil {
return acc.(Value), nil
}
return nil, errors.Errorf("Empty input to min")
},
)
}
// String returns a string representation of the expression.
func (e *ReduceExpr) String() string {
return fmt.Sprintf(e.format, e.a)
}
// Eval returns the subject
func (e *ReduceExpr) Eval(local Scope) (_ Value, err error) {
a, err := e.a.Eval(local)
if err != nil {
return nil, WrapContext(err, e, local)
}
if s, ok := a.(Set); ok {
acc, err := e.init(s)
if err != nil {
return nil, WrapContext(err, e, local)
}
for i := s.Enumerator(); i.MoveNext(); {
f, err := e.f.Eval(local)
if err != nil {
return nil, WrapContext(err, e, local)
}
v, err := SetCall(f.(Closure), i.Current())
if err != nil {
return nil, WrapContext(err, e, local)
}
acc, err = e.reduce(acc, v)
if err != nil {
return nil, WrapContext(err, e, local)
}
}
return e.output(acc)
}
return nil, errors.Errorf("Not a set")
}