deltas.Group(GroupName("^[^:]*"))

ledger/deltas.go

@@ -6,6 +6,14 @@ import (
 
 type Deltas []Delta
 
+func (deltas Deltas) Group(group ...Group) Deltas {
+	result := make(Deltas, 0, len(deltas))
+	for i := range deltas {
+		result = append(result, Groups(group).Each(deltas[i]))
+	}
+	return result
+}
+
 func (deltas Deltas) Like(like ...Like) Deltas {
 	result := make(Deltas, 0, len(deltas))
 	for i := range deltas {

ledger/deltas_test.go

@@ -3,6 +3,32 @@ package ledger
 import "testing"
 
 func TestDeltas(t *testing.T) {
+	t.Run("Groups", func(t *testing.T) {
+		deltas := Deltas{
+			{Name: "a1"},
+			{Name: "b1"},
+			{Name: "b2"},
+			{Name: "b3"},
+		}
+
+		deltas = deltas.Group(GroupName("^."))
+		if len(deltas) != 4 {
+			t.Error(len(deltas))
+		}
+		if deltas[0].Name != "a" {
+			t.Error(deltas[0].Name)
+		}
+		if deltas[1].Name != "b" {
+			t.Error(deltas[1].Name)
+		}
+		if deltas[2].Name != "b" {
+			t.Error(deltas[2].Name)
+		}
+		if deltas[3].Name != "b" {
+			t.Error(deltas[3].Name)
+		}
+	})
+
 	t.Run("balances", func(t *testing.T) {
 		deltas := Deltas{
 			{Name: "a", Value: 0},

ledger/group.go

@@ -4,6 +4,15 @@ import "regexp"
 
 type Group func(Delta) Delta
 
+type Groups []Group
+
+func (groups Groups) Each(d Delta) Delta {
+	for i := range groups {
+		d = groups[i](d)
+	}
+	return d
+}
+
 func GroupDate(pattern string) Group {
 	p := regexp.MustCompile(pattern)
 	return func(d Delta) Delta {