From 069812e0eee1b9e462ca3cc6cfc6d51ca94563fe Mon Sep 17 00:00:00 2001
From: donutloop <marcel.edmund.franke@gmail.com>
Date: Tue, 27 Feb 2024 03:36:26 +0100
Subject: [PATCH] Hashmap: Add FilterByValue (#184)

The FilterByValue function is a method defined on the HashMap type. It generates a new HashMap
containing only the elements that satisfy a specified condition,
as determined by a predicate function applied to each element's value.

Note: Will add later doc
---
 datastructure/hashmap/hashmap.go      | 24 ++++++++++++++++++++++++
 datastructure/hashmap/hashmap_test.go | 21 +++++++++++++++++++++
 2 files changed, 45 insertions(+)

diff --git a/datastructure/hashmap/hashmap.go b/datastructure/hashmap/hashmap.go
index d754476..b8e7f3d 100644
--- a/datastructure/hashmap/hashmap.go
+++ b/datastructure/hashmap/hashmap.go
@@ -123,6 +123,25 @@ func (hm *HashMap) Iterate(iteratee func(key, value any)) {
 	}
 }
 
+// FilterByValue returns a filtered HashMap.
+// If any value is not matching the perdicate function then it returns nil
+// otherwise it returns the HashMap with selected values.
+func (hm *HashMap) FilterByValue(perdicate func(value any) bool) *HashMap {
+	var filteredHM *HashMap
+	if hm.size > 0 {
+		for i := 0; i < len(hm.table); i++ {
+			item := hm.table[i]
+			if item != nil && perdicate(item.value) {
+				if filteredHM == nil {
+					filteredHM = NewHashMap()
+				}
+				filteredHM.Put(item.key, item.value)
+			}
+		}
+	}
+	return filteredHM
+}
+
 // Keys returns a slice of the hashmap's keys (random order)
 func (hm *HashMap) Keys() []any {
 	keys := make([]any, int(hm.size))
@@ -168,6 +187,11 @@ func (hm *HashMap) resize() {
 	}
 }
 
+// Size returns current size of Hashmap
+func (hm *HashMap) Size() uint64 {
+	return hm.size
+}
+
 func (hm *HashMap) hash(key any) uint64 {
 	h := fnv.New64a()
 	_, _ = h.Write([]byte(fmt.Sprintf("%v", key)))
diff --git a/datastructure/hashmap/hashmap_test.go b/datastructure/hashmap/hashmap_test.go
index 747af19..66ebe2b 100644
--- a/datastructure/hashmap/hashmap_test.go
+++ b/datastructure/hashmap/hashmap_test.go
@@ -105,3 +105,24 @@ func TestHashMap_GetOrDefault(t *testing.T) {
 	assert.Equal(1, hm.GetOrDefault("a", 5))
 	assert.Equal(5, hm.GetOrDefault("d", 5))
 }
+
+func TestHashMap_FilterByValue(t *testing.T) {
+	t.Parallel()
+
+	assert := internal.NewAssert(t, "TestHashMap_FilterByValue")
+
+	hm := NewHashMap()
+
+	hm.Put("a", 1)
+	hm.Put("b", 2)
+	hm.Put("c", 3)
+	hm.Put("d", 4)
+	hm.Put("e", 5)
+	hm.Put("f", 6)
+
+	filteredHM := hm.FilterByValue(func(value any) bool {
+		return value.(int) == 1 || value.(int) == 3
+	})
+
+	assert.Equal(uint64(2), filteredHM.Size())
+}