From c87f3f88b7059e4a48052ef81efe7c5a5a27dcc6 Mon Sep 17 00:00:00 2001
From: Ruidy <rnemausat@newstore.com>
Date: Wed, 10 Aug 2022 16:57:00 +0200
Subject: [PATCH] add flatmap

Signed-off-by: Ruidy <rnemausat@newstore.com>
---
 docs/content/collections/flatmap.md | 23 +++++++++++++++++++++++
 flatmap.go                          | 11 +++++++++++
 flatmap_test.go                     | 16 ++++++++++++++++
 3 files changed, 50 insertions(+)
 create mode 100644 docs/content/collections/flatmap.md
 create mode 100644 flatmap.go
 create mode 100644 flatmap_test.go

diff --git a/docs/content/collections/flatmap.md b/docs/content/collections/flatmap.md
new file mode 100644
index 0000000..80033fa
--- /dev/null
+++ b/docs/content/collections/flatmap.md
@@ -0,0 +1,23 @@
+---
+title: "Flatmap"
+date: 2022-08-10T16:49:56+02:00
+draft: false
+---
+
+Flatmap flattens the input slice element into the new slice. FlatMap maps every element with the help of a mapper function, then flattens the input slice element into the new slice.
+
+```go
+package main
+
+import (
+	"fmt"
+	u "github.com/rjNemo/underscore"
+)
+
+func main() {
+  nums := []int{1, 2, 3, 4}
+  mapper := func(n int) []int { return []int{(n - 1) * n, (n) * n} }
+  res := u.Flatmap(nums, mapper)
+  fmt.Println(res) // {0, 1, 2, 4, 6, 9, 12, 16}
+}
+```
diff --git a/flatmap.go b/flatmap.go
new file mode 100644
index 0000000..1ce9c80
--- /dev/null
+++ b/flatmap.go
@@ -0,0 +1,11 @@
+package underscore
+
+// Flatmap flatten the input slice element into the new slice. FlatMap maps every element with the help of a mapper function, then flattens the input slice element into the new slice.
+func Flatmap[T any](values []T, mapper func(n T) []T) []T {
+	res := make([]T, 0)
+	for _, v := range values {
+		vs := mapper(v)
+		res = append(res, vs...)
+	}
+	return res
+}
diff --git a/flatmap_test.go b/flatmap_test.go
new file mode 100644
index 0000000..29fdb10
--- /dev/null
+++ b/flatmap_test.go
@@ -0,0 +1,16 @@
+package underscore_test
+
+import (
+	"testing"
+
+	u "github.com/rjNemo/underscore"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestFlatmap(t *testing.T) {
+	nums := []int{1, 2, 3, 4}
+	transform := func(n int) []int { return []int{(n - 1) * n, (n) * n} }
+	want := []int{0, 1, 2, 4, 6, 9, 12, 16}
+
+	assert.Equal(t, want, u.Flatmap(nums, transform))
+}