adds a sliceutils method to flatten a slice of slice of type I to a single level slice of type I (#20)

Co-authored-by: Vincent Hoen <vincent.hoen@ext.groupepvcp.com>

Author: vhoen

docs/sliceutils/flatten.md

@@ -0,0 +1,24 @@
+# Flatten
+
+`Flatten[I any](input [][]I) []I`
+
+Flatten - receives a slice of slice of type I and flattens it to a slice of type I.
+
+```go
+package main
+
+import (
+	"github.com/Goldziher/go-utils/sliceutils"
+)
+
+func main() {
+	items := [][]int{
+		{1, 2, 3, 4},
+		{5, 6},
+		{7, 8},
+		{9, 10, 11},
+	}
+
+	flattened := sliceutils.Flatten(items) //[]int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11}
+}
+```

mkdocs.yml

@@ -16,6 +16,7 @@ nav:
       - sliceutils/findIndexesOf.md
       - sliceutils/findLastIndex.md
       - sliceutils/findLastIndexOf.md
+      - sliceutils/flatten.md
       - sliceutils/forEach.md
       - sliceutils/includes.md
       - sliceutils/insert.md

sliceutils/sliceutils.go

@@ -338,3 +338,14 @@ func Pluck[I any, O any](input []I, getter func(I) *O) []O {
 
 	return output
 }
+
+// Flatten - receives a slice of slice of type I and flattens it to a slice of type I.
+func Flatten[I any](input [][]I) []I {
+	var output []I
+
+	ForEach(input, func(item []I, index int, slice [][]I) {
+		output = append(output, item...)
+	})
+
+	return output
+}

sliceutils/sliceutils_test.go

@@ -267,3 +267,16 @@ func TestPluck(t *testing.T) {
 		return &item.Value
 	}))
 }
+
+func TestFlatten(t *testing.T) {
+	items := [][]int{
+		{1, 2, 3, 4},
+		{5, 6},
+		{7, 8},
+		{9, 10, 11},
+	}
+
+	flattened := sliceutils.Flatten(items)
+
+	assert.Equal(t, []int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11}, flattened)
+}