diff --git a/dataframe_group.go b/dataframe_group.go
new file mode 100644
index 0000000000000000000000000000000000000000..e464447624a62296567b9d731b76e2e28742b786
--- /dev/null
+++ b/dataframe_group.go
@@ -0,0 +1,28 @@
+package pandas
+
+import (
+	"gitee.com/quant1x/pandas/stat"
+)
+
+// Group 分组
+func (self DataFrame) Group(columnName string, filter func(kind stat.Type, e any) bool) DataFrame {
+	series := self.Col(columnName)
+	if series.Len() == 0 {
+		return self
+	}
+	t := series.Type()
+	indexes := []int{}
+	series.Apply(func(idx int, v any) {
+		ok := filter(t, v)
+		if ok {
+			indexes = append(indexes, idx)
+		}
+	})
+	ranges := stat.IntsToRanges(indexes)
+	df := DataFrame{}
+	for _, r := range ranges {
+		tmp := self.SelectRows(r)
+		df = df.Concat(tmp)
+	}
+	return df
+}
diff --git a/dataframe_group_test.go b/dataframe_group_test.go
new file mode 100644
index 0000000000000000000000000000000000000000..0317de459d9167556d19f5437604c83794507c8f
--- /dev/null
+++ b/dataframe_group_test.go
@@ -0,0 +1,40 @@
+package pandas
+
+import (
+	"fmt"
+	"gitee.com/quant1x/pandas/stat"
+	"testing"
+)
+
+func TestDataFrame_Group(t *testing.T) {
+	type testStruct struct {
+		A string
+		B int
+		C bool
+		D float64
+	}
+	data := []testStruct{
+		{"a", 1, true, 0.0},
+		{"b", 2, false, 0.5},
+		{"b", 3, false, 3.5},
+		{"b", 4, false, 2.5},
+		{"b", 5, false, 1.5},
+		{"a", 6, true, 0.0},
+		{"a", 7, true, 0.0},
+		{"a", 8, true, 0.0},
+		{"a", 9, true, 0.0},
+		{"a", 10, true, 0.0},
+		{"a", 11, true, 0.0},
+	}
+	df := LoadStructs(data)
+	fmt.Println(df)
+
+	df1 := df.Group("A", func(kind stat.Type, e any) bool {
+		v := stat.AnyToString(e)
+		if v == "b" {
+			return true
+		}
+		return false
+	})
+	fmt.Println(df1)
+}
diff --git a/dataframe_subset.go b/dataframe_subset.go
index 747f2778b9ca163588bada5fa8fb5aedb3c99262..b62ea09764946b4b53595c5d3b12f10bd5475077 100644
--- a/dataframe_subset.go
+++ b/dataframe_subset.go
@@ -26,7 +26,13 @@ func (self DataFrame) Subset(start, end int) DataFrame {
 	}
 }
 
-// Select 选择一段记录
+// Sub 选择一个子集, start end 支持从后到前选择
+func (self DataFrame) Sub(start, end int) DataFrame {
+	sl := stat.RangeFinite(start, end)
+	return self.SelectRows(sl)
+}
+
+// SelectRows 选择一段记录
 func (self DataFrame) SelectRows(p stat.ScopeLimit) DataFrame {
 	columns := []stat.Series{}
 	for i := range self.columns {
diff --git a/dataframe_xstring.go b/dataframe_xstring.go
index 78fbd087e0289b060a001fd260e0d8d2daa24cb0..c21015d1a42d2431a022137aa66dadb3a671915c 100644
--- a/dataframe_xstring.go
+++ b/dataframe_xstring.go
@@ -36,7 +36,7 @@ func (self DataFrame) print(
 		str = fmt.Sprintf("%s error: %v", class, self.Err)
 		return
 	}
-	nMinRows := int(maxRows / 2)
+	nMinRows := maxRows / 2
 	nTotal := 0
 	nrows, ncols := self.Dims()
 	if nrows == 0 || ncols == 0 {
@@ -80,10 +80,10 @@ func (self DataFrame) print(
 		} else if i == nMinRows+1 && shortening {
 			// 跳过
 			rowNumbersOffset -= 1
-		} else if i < nMinRows+1 {
-			add = strconv.Itoa(i-1+rowNumbersOffset) + ":"
-		} else {
+		} else if i >= nMinRows+1 && shortening {
 			add = strconv.Itoa(nrows-maxRows+i-1+rowNumbersOffset) + ":"
+		} else {
+			add = strconv.Itoa(i-1+rowNumbersOffset) + ":"
 		}
 		//fmt.Println(i)
 		records[i] = append([]string{add}, records[i]...)