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filter.go
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filter.go
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package yogofn
import "reflect"
// Filter takes a boolean predicate and a collection (i.e. an Array or Slice),
// resulting in a reduced output slice where each element passes the predicate.
// The predicate, the input collection and the output collection are all
// typed as interface{}. The result is almost always going to require a cast.
//
// For instance, filtering out names with "Z" might be:
//
// nonZs := Filter(
// func(name string) bool { return !strings.Contains(name,"Z"); },
// names).([]string)
//
func Filter(predicate, collection interface{}) interface{} {
// common optimizations
{
switch f1 := predicate.(type) {
case func(string) bool:
if ss, ok := collection.([]string); ok {
result := make([]string, 0, len(ss))
for _, s := range ss {
if f1(s) {
result = append(result, s)
}
}
return result
}
case func(int) bool:
if ns, ok := collection.([]int); ok {
result := make([]int, 0, len(ns))
for _, n := range ns {
if f1(n) {
result = append(result, n)
}
}
return result
}
case func(float64) bool:
if fs, ok := collection.([]float64); ok {
result := make([]float64, 0, len(fs))
for _, f := range fs {
if f1(f) {
result = append(result, f)
}
}
return result
}
}
}
typecheck(collection, reflect.Array, reflect.Slice)
typecheck(predicate, reflect.Func)
if pT := reflect.TypeOf(predicate); pT.NumIn() != 1 || pT.NumOut() != 1 || pT.Out(0).Kind() != reflect.Bool {
panic("Filter expected predicate: (func(T) bool), received: (" + pT.String() + ")")
}
collectionValue := reflect.ValueOf(collection)
predicateValue := reflect.ValueOf(predicate)
length := collectionValue.Len()
// Make empty result slice
resultType := reflect.SliceOf(reflect.TypeOf(collection).Elem())
resultValue := reflect.Zero(resultType)
for i := 0; i < length; i++ {
v := collectionValue.Index(i)
if predicateValue.Call([]reflect.Value{v})[0].Bool() {
resultValue = reflect.Append(resultValue, v)
}
}
return resultValue.Interface()
}