add test for symbols sorted by order of frequency

Signed-off-by: Callum Styan <[email protected]>

index/index.go

@@ -64,9 +64,9 @@ type symbolFrequencyPair struct {
 
 type symbolFrequencylist []symbolFrequencyPair
 
-func (s symbolFrequencylist) Len() int           { return len(s) }
-func (s symbolFrequencylist) Swap(i, j int)      { s[i], s[j] = s[j], s[i] }
-func (s symbolFrequencylist) Less(i, j int) bool { return s[i].frequency < s[j].frequency }
+func (s symbolFrequencylist) Len() int              { return len(s) }
+func (s symbolFrequencylist) Swap(i, j int)         { s[i], s[j] = s[j], s[i] }
+func (s symbolFrequencylist) Greater(i, j int) bool { return s[i].frequency > s[j].frequency }
 
 type indexWriterStage uint8
 
@@ -355,7 +355,14 @@ func (w *Writer) AddSymbols(sym map[string]int) error {
 	for k, v := range sym {
 		symbols = append(symbols, symbolFrequencyPair{k, v})
 	}
-	sort.Sort(sort.Reverse(symbols))
+	sort.Slice(symbols, func(i, j int) bool {
+		// We get the symbols back as a map so we need to be sure
+		// to sort by symbol if the frequencies are the same.
+		if symbols[i].frequency == symbols[j].frequency {
+			return symbols[i].symbol > symbols[j].symbol
+		}
+		return symbols.Greater(i, j)
+	})
 
 	const headerSize = 4
 
@@ -874,7 +881,7 @@ func (r *Reader) Symbols() (map[string]int, error) {
 		res[s] = 0
 	}
 	for _, s := range r.symbolSlice {
-		res[s] = struct{}{}
+		res[s] = 0
 	}
 	return res, nil
 }

index/index_test.go

@@ -232,6 +232,48 @@ func TestIndexRW_Postings(t *testing.T) {
 	testutil.Ok(t, ir.Close())
 }
 
+func TestIndexRW_SymbolsOrder(t *testing.T) {
+	dir, err := ioutil.TempDir("", "test_index_order")
+	testutil.Ok(t, err)
+	defer os.RemoveAll(dir)
+
+	fn := filepath.Join(dir, "index")
+
+	iw, err := NewWriter(fn)
+	testutil.Ok(t, err)
+
+	err = iw.AddSymbols(map[string]int{
+		"a": 1,
+		"b": 2,
+		"c": 1,
+		"2": 4,
+		"3": 5,
+		"4": 3,
+	})
+
+	testutil.Ok(t, err)
+	testutil.Ok(t, iw.Close())
+
+	exp := []string{"3", "2", "4", "b", "c", "a"}
+
+	ir, err := NewFileReader(fn)
+	testutil.Ok(t, err)
+
+	err = ir.readSymbols(int(ir.toc.symbols))
+	testutil.Ok(t, err)
+
+	s, err := ir.Symbols()
+	t.Logf("symbols: %+v", s)
+
+	testutil.Equals(t, len(ir.symbolSlice), len(exp))
+
+	for i := range ir.symbolSlice {
+		testutil.Equals(t, ir.symbolSlice[i], exp[i])
+	}
+
+	testutil.Ok(t, ir.Close())
+}
+
 func TestPersistence_index_e2e(t *testing.T) {
 	dir, err := ioutil.TempDir("", "test_persistence_e2e")
 	testutil.Ok(t, err)