Add support for ignore-columns flag as an inverse of columns flag (fixes

 #23)

cmd/config.go

@@ -51,6 +51,13 @@ func NewContext(
 		return nil, fmt.Errorf("base-file and delta-file columns count do not match")
 	}
 
+	if len(ignoreValueColumnPositions) > 0 && len(valueColumnPositions) > 0 {
+		return nil, fmt.Errorf("only one of --columns or --ignore-columns")
+	}
+	if len(ignoreValueColumnPositions) > 0 {
+		valueColumnPositions = inferValueColumns(baseRecordCount, ignoreValueColumnPositions)
+	}
+
 	baseFile, err := fs.Open(baseFilename)
 	if err != nil {
 		return nil, err
@@ -140,6 +147,24 @@ func (c *Context) validate() error {
 	return nil
 }
 
+func inferValueColumns(recordCount int, ignoreValueColumns []int) digest.Positions {
+	lookupMap := make(map[int]struct{})
+	for _, pos := range ignoreValueColumns {
+		lookupMap[pos] = struct{}{}
+	}
+
+	valueColumns := make(digest.Positions, 0)
+	if len(ignoreValueColumns) > 0 {
+		for i := 0; i < recordCount; i++ {
+			if _, exists := lookupMap[i]; !exists {
+				valueColumns = append(valueColumns, i)
+			}
+		}
+	}
+
+	return valueColumns
+}
+
 func assertAll(elements []int, assertFn func(element int) bool) bool {
 	for _, el := range elements {
 		if !assertFn(el) {

cmd/config_test.go

@@ -300,6 +300,24 @@ func TestNewContext(t *testing.T) {
 			assert.EqualError(t, err, "base-file and delta-file columns count do not match")
 		})
 	})
+
+	t.Run("should pass only one of columns or ignore columns", func(t *testing.T) {
+		fs := afero.NewMemMapFs()
+		setupFiles(t, fs)
+
+		_, err := cmd.NewContext(
+			fs,
+			nil,
+			[]int{0},
+			[]int{0},
+			nil,
+			"jSOn",
+			"/base.csv",
+			"/delta.csv",
+		)
+
+		assert.EqualError(t, err, "only one of --columns or --ignore-columns")
+	})
 }
 
 func TestConfig_DigestConfig(t *testing.T) {
@@ -326,17 +344,49 @@ func TestConfig_DigestConfig(t *testing.T) {
 
 		assert.NoError(t, err)
 		assert.NotNil(t, baseConfig.Reader)
-		assert.Equal(t, baseConfig.Value, valueColumns)
-		assert.Equal(t, baseConfig.Key, primaryColumns)
-		assert.Equal(t, baseConfig.Include, includeColumns)
+		assert.Equal(t, valueColumns, baseConfig.Value)
+		assert.Equal(t, primaryColumns, baseConfig.Key)
+		assert.Equal(t, includeColumns, baseConfig.Include)
+
+		deltaConfig, err := ctx.DeltaDigestConfig()
+
+		assert.NoError(t, err)
+		assert.NotNil(t, deltaConfig.Reader)
+		assert.Equal(t, valueColumns, deltaConfig.Value)
+		assert.Equal(t, primaryColumns, deltaConfig.Key)
+		assert.Equal(t, includeColumns, deltaConfig.Include)
+	})
+	t.Run("should infer values columns as inverse of ignore columns digest ctx", func(t *testing.T) {
+		fs := afero.NewMemMapFs()
+		setupFiles(t, fs)
+
+		ignoreValueColumns := digest.Positions{0, 1, 2}
+		primaryColumns := digest.Positions{0, 1}
+		ctx, err := cmd.NewContext(
+			fs,
+			primaryColumns,
+			nil,
+			ignoreValueColumns,
+			nil,
+			"jSOn",
+			"/base.csv",
+			"/delta.csv",
+		)
+		assert.NoError(t, err)
+
+		baseConfig, err := ctx.BaseDigestConfig()
+
+		assert.NoError(t, err)
+		assert.NotNil(t, baseConfig.Reader)
+		assert.Equal(t, digest.Positions{3}, baseConfig.Value)
+		assert.Equal(t, primaryColumns, baseConfig.Key)
 
 		deltaConfig, err := ctx.DeltaDigestConfig()
 
 		assert.NoError(t, err)
 		assert.NotNil(t, deltaConfig.Reader)
-		assert.Equal(t, deltaConfig.Value, valueColumns)
-		assert.Equal(t, deltaConfig.Key, primaryColumns)
-		assert.Equal(t, deltaConfig.Include, includeColumns)
+		assert.Equal(t, digest.Positions{3}, deltaConfig.Value)
+		assert.Equal(t, primaryColumns, deltaConfig.Key)
 	})
 }
 func setupFiles(t *testing.T, fs afero.Fs) {