add Interleave helper to slices (#155)

* initial interleave working

* add nil case

* Update README.md

Co-authored-by: Samuel Berthe <dev@samuel-berthe.fr>

README.md

@@ -73,6 +73,7 @@ Supported helpers for slices:
 - [Chunk](#chunk)
 - [PartitionBy](#partitionby)
 - [Flatten](#flatten)
+- [Interleave](#interleave)
 - [Shuffle](#shuffle)
 - [Reverse](#reverse)
 - [Fill](#fill)
@@ -499,6 +500,15 @@ flat := lo.Flatten[int]([][]int{{0, 1}, {2, 3, 4, 5}})
 
 [[play](https://go.dev/play/p/rbp9ORaMpjw)]
 
+### Interleave
+
+Round-robbin alternating input slices and sequentially appending value at index into result.
+
+```go
+interleaved := lo.Interleave[int]([]int{1, 4, 7}, []int{2, 5, 8}, []int{3, 6, 9})
+// []int{1, 2, 3, 4, 5, 6, 7, 8, 9}
+```
+
 ### Shuffle
 
 Returns an array of shuffled values. Uses the Fisher-Yates shuffle algorithm.

slice.go

@@ -546,3 +546,40 @@ func IsSortedByKey[T any, K constraints.Ordered](collection []T, iteratee func(T
 
 	return true
 }
+
+// Interleave round-robbin alternating input slices and sequentially appending value at index into result
+func Interleave[T any](collections ...[]T) []T {
+	if len(collections) == 0 {
+		return []T{}
+	}
+
+	maxSize := 0
+	totalSize := 0
+	for _, c := range collections {
+		size := len(c)
+		totalSize += size
+		if size > maxSize {
+			maxSize = size
+		}
+	}
+
+	if maxSize == 0 {
+		return []T{}
+	}
+
+	result := make([]T, totalSize)
+
+	resultIdx := 0
+	for i := 0; i < maxSize; i++ {
+		for j := range collections {
+			if len(collections[j])-1 < i {
+				continue
+			}
+
+			result[resultIdx] = collections[j][i]
+			resultIdx++
+		}
+	}
+
+	return result
+}

slice_test.go

@@ -3,6 +3,7 @@ package lo
 import (
 	"fmt"
 	"math"
+	"reflect"
 	"strconv"
 	"strings"
 	"testing"
@@ -666,3 +667,49 @@ func TestIsSortedByKey(t *testing.T) {
 		return ret
 	}))
 }
+
+func TestInterleave(t *testing.T) {
+	tests := []struct {
+		name        string
+		collections [][]int
+		want        []int
+	}{
+		{
+			"nil",
+			[][]int{nil},
+			[]int{},
+		},
+		{
+			"empty",
+			[][]int{},
+			[]int{},
+		},
+		{
+			"empties",
+			[][]int{{}, {}},
+			[]int{},
+		},
+		{
+			"same length",
+			[][]int{{1, 3, 5}, {2, 4, 6}},
+			[]int{1, 2, 3, 4, 5, 6},
+		},
+		{
+			"different length",
+			[][]int{{1, 3, 5, 6}, {2, 4}},
+			[]int{1, 2, 3, 4, 5, 6},
+		},
+		{
+			"many slices",
+			[][]int{{1}, {2, 5, 8}, {3, 6}, {4, 7, 9, 10}},
+			[]int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10},
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := Interleave(tt.collections...); !reflect.DeepEqual(got, tt.want) {
+				t.Errorf("Interleave() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}