Merge pull request #20 from onozaty/develop/v1.13.0

Develop v1.13.0

README.md

@@ -13,6 +13,7 @@
 * [concat](#concat) Concat CSV files.
 * [count](#count) Count the number of records.
 * [exclude](#exclude) Exclude rows by included in another CSV file.
+* [group](#group) Aggregate by group.
 * [filter](#filter) Filter rows by condition.
 * [head](#head) Show head few rows.
 * [header](#header) Show header.
@@ -349,6 +350,66 @@ col1,col2
 4,D
 ```
 
+## group
+
+Group by the value of the specified column and perform aggregation.  
+
+Currently, only counting is supported.  
+It's like `GROUP BY` + `COUNT` in SQL.
+
+### Usage
+
+```
+csvt group -i INPUT -c COLUMN [--count-column COUNT_COLUMN] -o OUTPUT
+```
+
+```
+Usage:
+  csvt group [flags]
+
+Flags:
+  -i, --input string          Input CSV file path.
+  -c, --column string         Name of the column to use for grouping.
+      --count-column string   (optional) Column name for the number of records. (default "COUNT")
+  -o, --output string         Output CSV file path.
+  -h, --help                  help for group
+```
+
+### Example
+
+The contents of `input.csv`.
+
+```
+col1,col2
+1,B
+2,B
+3,A
+4,D
+5,C
+6,D
+7,D
+8,E
+9,A
+10,D
+```
+
+Group the rows by the value of `col2` and aggregate the number of rows.
+
+```
+$ csvt group -i input.csv -c col2 -o output.csv
+```
+
+The contents of the created `output.csv`.
+
+```
+col2,COUNT
+A,2
+B,2
+C,1
+D,4
+E,1
+```
+
 ## filter
 
 Create a new CSV file by filtering the input CSV file to rows that match the conditions.

cmd/group.go

@@ -0,0 +1,115 @@
+package cmd
+
+import (
+	"io"
+	_sort "sort"
+	"strconv"
+
+	"github.com/onozaty/csvt/csv"
+	"github.com/pkg/errors"
+	"github.com/spf13/cobra"
+)
+
+func newGroupCmd() *cobra.Command {
+
+	gcountCmd := &cobra.Command{
+		Use:   "group",
+		Short: "Aggregate by group",
+		RunE: func(cmd *cobra.Command, args []string) error {
+
+			format, err := getFlagBaseCsvFormat(cmd.Flags())
+			if err != nil {
+				return err
+			}
+
+			inputPath, _ := cmd.Flags().GetString("input")
+			targetColumnName, _ := cmd.Flags().GetString("column")
+			outputPath, _ := cmd.Flags().GetString("output")
+			countColumnName, _ := cmd.Flags().GetString("count-column")
+
+			// 引数の解析に成功した時点で、エラーが起きてもUsageは表示しない
+			cmd.SilenceUsage = true
+
+			return runGroupCount(
+				format,
+				inputPath,
+				targetColumnName,
+				countColumnName,
+				outputPath)
+		},
+	}
+
+	gcountCmd.Flags().StringP("input", "i", "", "Input CSV file path.")
+	gcountCmd.MarkFlagRequired("input")
+	gcountCmd.Flags().StringP("column", "c", "", "Name of the column to use for grouping.")
+	gcountCmd.MarkFlagRequired("column")
+	gcountCmd.Flags().StringP("count-column", "", "COUNT", "(optional) Column name for the number of records.")
+	gcountCmd.Flags().StringP("output", "o", "", "Output CSV file path.")
+	gcountCmd.MarkFlagRequired("output")
+
+	return gcountCmd
+}
+
+func runGroupCount(format csv.Format, inputPath string, targetColumnName string, countColumnName string, outputPath string) error {
+
+	reader, writer, close, err := setupInputOutput(inputPath, outputPath, format)
+	if err != nil {
+		return err
+	}
+	defer close()
+
+	err = groupCount(reader, targetColumnName, countColumnName, writer)
+	if err != nil {
+		return err
+	}
+
+	return writer.Flush()
+}
+
+func groupCount(reader csv.CsvReader, targetColumnName string, countColumnName string, writer csv.CsvWriter) error {
+
+	// ヘッダ
+	columnNames, err := reader.Read()
+	if err != nil {
+		return errors.Wrap(err, "failed to read the CSV file")
+	}
+
+	targetColumnIndex, err := getTargetColumnIndex(columnNames, targetColumnName)
+	if err != nil {
+		return err
+	}
+
+	counter := map[string]int{}
+
+	for {
+		row, err := reader.Read()
+		if err == io.EOF {
+			break
+		}
+		if err != nil {
+			return errors.Wrap(err, "failed to read the CSV file")
+		}
+
+		val := row[targetColumnIndex]
+		counter[val] = counter[val] + 1
+	}
+
+	if err := writer.Write([]string{targetColumnName, countColumnName}); err != nil {
+		return err
+	}
+
+	// グループ化した値でソートして出力
+	keys := []string{}
+	for k := range counter {
+		keys = append(keys, k)
+	}
+	_sort.Strings(keys)
+
+	for _, k := range keys {
+		if err := writer.Write([]string{k, strconv.Itoa(counter[k])}); err != nil {
+			return err
+		}
+	}
+
+	return nil
+}