From e33476ea5ca3a00a89d3cafe87156a332ac244e2 Mon Sep 17 00:00:00 2001
From: Leon Mika <lmika@lmika.org>
Date: Sat, 5 Sep 2026 09:23:54 +1000
Subject: [PATCH] Added FilterMap

---
 moslice/filter.go      | 19 +++++++++++++++++++
 moslice/filter_test.go | 24 +++++++++++++++++++++++-
 2 files changed, 42 insertions(+), 1 deletion(-)

diff --git a/moslice/filter.go b/moslice/filter.go
index cd3bbbb..07900e8 100644
--- a/moslice/filter.go
+++ b/moslice/filter.go
@@ -16,3 +16,22 @@ func Filter[T any](ts []T, predicate func(t T) bool) []T {
 	}
 	return filteredTs
 }
+
+// FilterMap returns a mapped slice containing all the elements of ts for which the passed in
+// predicate returns true.  If no items match the predicate, the function will return
+// an empty slice.  If ts is nil, the function will also return nil.
+func FilterMap[T, U any](ts []T, predicate func(t T) (U, bool)) []U {
+	if ts == nil {
+		return nil
+	}
+
+	filteredUs := make([]U, 0)
+	for _, t := range ts {
+		u, ok := predicate(t)
+		if !ok {
+			continue
+		}
+		filteredUs = append(filteredUs, u)
+	}
+	return filteredUs
+}
diff --git a/moslice/filter_test.go b/moslice/filter_test.go
index 1d4ae28..f77a02f 100644
--- a/moslice/filter_test.go
+++ b/moslice/filter_test.go
@@ -1,10 +1,12 @@
 package moslice_test
 
 import (
-	"lmika.dev/pkg/modash/moslice"
+	"fmt"
 	"strings"
 	"testing"
 
+	"lmika.dev/pkg/modash/moslice"
+
 	"github.com/stretchr/testify/assert"
 )
 
@@ -27,3 +29,23 @@ func TestFilter(t *testing.T) {
 		assert.Equal(t, []int{}, moslice.Filter([]int{}, func(x int) bool { return x%2 == 0 }))
 	})
 }
+
+func TestFilterMap(t *testing.T) {
+	var (
+		ints = []int{1, 2, 3, 4, 5}
+		strs = []string{"foo", "bar", "baz"}
+	)
+
+	t.Run("should filter items matching the predicate", func(t *testing.T) {
+		assert.Equal(t, []string{"2", "4"}, moslice.FilterMap(ints, func(x int) (string, bool) { return fmt.Sprint(x), x%2 == 0 }))
+		assert.Equal(t, []int{3, 3}, moslice.FilterMap(strs, func(x string) (int, bool) { return len(x), strings.Contains(x, "b") }))
+	})
+
+	t.Run("should moslice nil if the passed in slice is nil", func(t *testing.T) {
+		assert.Nil(t, moslice.FilterMap(nil, func(x int) (string, bool) { return fmt.Sprint(x), x%2 == 0 }))
+	})
+
+	t.Run("should return empty slice if the passed in slice is empty slice", func(t *testing.T) {
+		assert.Equal(t, []string{}, moslice.FilterMap([]int{}, func(x int) (string, bool) { return fmt.Sprint(x), x%2 == 0 }))
+	})
+}