fn: Added map functions

Signed-off-by: Ononiwu Maureen <59079323+Chinwendu20@users.noreply.github.com>

fn/map.go

@@ -0,0 +1,44 @@
+package fn
+
+import (
+	"fmt"
+
+	"golang.org/x/exp/maps"
+)
+
+// KeySet converts a map into a Set containing the keys of the map.
+func KeySet[K comparable, V any](m map[K]V) Set[K] {
+	return NewSet(maps.Keys(m)...)
+}
+
+// NewSubMapIntersect returns a sub-map of `m` containing only the keys found in
+// both `m` and the `keys` slice.
+func NewSubMapIntersect[K comparable, V any](m map[K]V, keys []K) map[K]V {
+	result := make(map[K]V)
+	for _, k := range keys {
+		v, ok := m[k]
+		if !ok {
+			continue
+		}
+
+		result[k] = v
+	}
+
+	return result
+}
+
+// NewSubMap creates a sub-map from a given map using specified keys. It errors
+// if any of the keys is not found in the map.
+func NewSubMap[K comparable, V any](m map[K]V, keys []K) (map[K]V, error) {
+	result := make(map[K]V, len(keys))
+	for _, k := range keys {
+		v, ok := m[k]
+		if !ok {
+			return nil, fmt.Errorf("NewSubMap: missing key %v", k)
+		}
+
+		result[k] = v
+	}
+
+	return result, nil
+}

fn/map_test.go

@@ -0,0 +1,135 @@
+package fn
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestKeySet(t *testing.T) {
+	testMap := map[string]int{"a": 1, "b": 2, "c": 3}
+	expected := NewSet([]string{"a", "b", "c"}...)
+
+	require.Equal(t, expected, KeySet(testMap))
+}
+
+// TestNewSubMap tests the NewSubMap function with various input cases.
+func TestNewSubMap(t *testing.T) {
+	tests := []struct {
+		name     string
+		original map[int]string
+		keys     []int
+		expected map[int]string
+		wantErr  bool
+	}{
+		{
+			name: "Successful submap creation",
+			original: map[int]string{
+				1: "apple",
+				2: "banana",
+				3: "cherry",
+			},
+			keys: []int{1, 3},
+			expected: map[int]string{
+				1: "apple",
+				3: "cherry",
+			},
+			wantErr: false,
+		},
+		{
+			name: "Key not found",
+			original: map[int]string{
+				1: "apple",
+				2: "banana",
+			},
+			keys:     []int{1, 4},
+			expected: nil,
+			wantErr:  true,
+		},
+		{
+			name: "Empty keys list",
+			original: map[int]string{
+				1: "apple",
+				2: "banana",
+			},
+			keys:     []int{},
+			expected: map[int]string{},
+			wantErr:  false,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			result, err := NewSubMap(tt.original, tt.keys)
+			if tt.wantErr {
+				require.ErrorContains(
+					t, err, "NewSubMap: missing key",
+				)
+
+				require.Nil(t, result)
+
+				return
+			}
+
+			require.NoError(t, err)
+			require.Equal(t, tt.expected, result)
+		})
+	}
+}
+
+// TestNewSubMapIntersect tests the NewSubMapIntersect function for correctness.
+func TestNewSubMapIntersect(t *testing.T) {
+	tests := []struct {
+		name     string
+		original map[int]string
+		keys     []int
+		expected map[int]string
+	}{
+		{
+			name: "Successful intersection",
+			original: map[int]string{
+				1: "apple",
+				2: "banana",
+				3: "cherry",
+				4: "date",
+			},
+			keys: []int{2, 3, 5},
+			expected: map[int]string{
+				2: "banana",
+				3: "cherry",
+			},
+		},
+		{
+			name: "No intersection",
+			original: map[int]string{
+				1: "apple",
+				2: "banana",
+			},
+			keys:     []int{3, 4},
+			expected: map[int]string{},
+		},
+		{
+			name:     "Empty original map",
+			original: map[int]string{},
+			keys:     []int{1, 2},
+			expected: map[int]string{},
+		},
+		{
+			name: "Empty keys list",
+			original: map[int]string{
+				1: "apple",
+				2: "banana",
+			},
+			keys:     []int{},
+			expected: map[int]string{},
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			require.Equal(
+				t, tt.expected,
+				NewSubMapIntersect(tt.original, tt.keys))
+		})
+	}
+}