file.Delta has sorted transactions with isSet

ledger/file.go

@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"io"
 	"os"
+	"sort"
 	"unicode"
 )
 
@@ -89,6 +90,10 @@ func (files Files) Deltas(like ...Like) (Deltas, error) {
 	if err != nil {
 		return nil, err
 	}
+	sort.Slice(transactions, func(i, j int) bool {
+		return fmt.Sprintf("%s %s", transactions[i].date, transactions[i].description) < fmt.Sprintf("%s %s", transactions[j].date, transactions[j].description)
+	})
+
 	result := make(Deltas, 0, len(transactions)*2)
 	for _, transaction := range transactions {
 		sums := map[string]float64{}