--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/sort.go	Sat Oct 13 21:42:11 2018 +0200
@@ -0,0 +1,43 @@
+/*
+ * Copyright (C) 2014-2018 Mikael Berthe <mikael@lilotux.net>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or (at
+ * your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307
+ * USA
+ */
+
+package main
+
+// Implement a sort interface for the list of duplicate groups
+type byGroupFileSize foListList
+
+func (a byGroupFileSize) Len() int      { return len(a) }
+func (a byGroupFileSize) Swap(i, j int) { a[i], a[j] = a[j], a[i] }
+func (a byGroupFileSize) Less(i, j int) bool {
+	// Since this is supposed to be used for duplicate lists,
+	// we use the size of the first file of the group.
+	if a[i][0].Size() == a[j][0].Size() {
+		return a[i][0].FilePath < a[j][0].FilePath
+	}
+	return a[i][0].Size() < a[j][0].Size()
+}
+
+// Implement a sort interface for a slice of files
+type byFilePathName FileObjList
+
+func (a byFilePathName) Len() int      { return len(a) }
+func (a byFilePathName) Swap(i, j int) { a[i], a[j] = a[j], a[i] }
+func (a byFilePathName) Less(i, j int) bool {
+	return a[i].FilePath < a[j].FilePath
+}