From 14fa41721fb577b493836880e01ba8ae85ab7da3 Mon Sep 17 00:00:00 2001
From: yuan <yuan@yuancoder.com>
Date: Thu, 14 Sep 2023 20:55:27 +0800
Subject: [PATCH 1/2] add Join func

---
 mr.go      | 13 +++++++++++++
 mr_test.go | 10 ++++++++++
 2 files changed, 23 insertions(+)

diff --git a/mr.go b/mr.go
index 6e40aa2..d98e957 100644
--- a/mr.go
+++ b/mr.go
@@ -1,5 +1,7 @@
 package mr
 
+import "strings"
+
 func Map[T any, R any](ts []T, f func(T) R) []R {
 	nt := make([]R, 0, len(ts))
 	for _, t := range ts {
@@ -107,3 +109,14 @@ func Paginate[T any](list []T, page, size int) []T {
 	}
 	return list[offset : offset+size]
 }
+
+func Join[T any](list []T, sep string, f func(T) string) string {
+	var builder strings.Builder
+	for i := 0; i < len(list); i++ {
+		if i > 0 {
+			builder.WriteString(sep)
+		}
+		builder.WriteString(f(list[i]))
+	}
+	return builder.String()
+}
diff --git a/mr_test.go b/mr_test.go
index 3ee234a..8504c1d 100644
--- a/mr_test.go
+++ b/mr_test.go
@@ -1,6 +1,7 @@
 package mr
 
 import (
+	"strconv"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
@@ -263,3 +264,12 @@ func TestPaginate(t *testing.T) {
 	result = Paginate(ts, 2, 2)
 	assert.Equal(t, expected, result)
 }
+
+func TestJoin(t *testing.T) {
+	str := Join(test_int_arr, ",", func(i int) string { return strconv.Itoa(i) })
+	assert.Equal(t, "1,2,3,4,5", str)
+
+	ts := []int{}
+	str = Join(ts, ",", func(i int) string { return strconv.Itoa(i) })
+	assert.Empty(t, str)
+}

From a7457ca363af2391e741562d9d17f4f74eb8bbe4 Mon Sep 17 00:00:00 2001
From: yuan <yuan@yuancoder.com>
Date: Tue, 2 Jan 2024 09:20:20 +0800
Subject: [PATCH 2/2] add keys func

---
 mr.go      |  8 ++++++++
 mr_test.go | 11 +++++++++++
 2 files changed, 19 insertions(+)

diff --git a/mr.go b/mr.go
index d98e957..5a68da0 100644
--- a/mr.go
+++ b/mr.go
@@ -120,3 +120,11 @@ func Join[T any](list []T, sep string, f func(T) string) string {
 	}
 	return builder.String()
 }
+
+func Keys[T any, KEY comparable](data map[KEY]T) []KEY {
+	var d []KEY
+	for k := range data {
+		d = append(d, k)
+	}
+	return d
+}
diff --git a/mr_test.go b/mr_test.go
index 8504c1d..b66f80b 100644
--- a/mr_test.go
+++ b/mr_test.go
@@ -273,3 +273,14 @@ func TestJoin(t *testing.T) {
 	str = Join(ts, ",", func(i int) string { return strconv.Itoa(i) })
 	assert.Empty(t, str)
 }
+
+func TestKeys(t *testing.T) {
+	td1 := map[string]int64{
+		"a": 1,
+		"b": 2,
+		"c": 3,
+	}
+	actual := Keys(td1)
+	expected := []string{"a", "b", "c"}
+	assert.EqualValuesf(t, expected, actual, "Expected %v atutal %v", expected, actual)
+}