Added flatten operator

pkg/yqlib/operator_flatten.go

@@ -0,0 +1,54 @@
+package yqlib
+
+import (
+	"fmt"
+
+	yaml "gopkg.in/yaml.v3"
+)
+
+type flattenPreferences struct {
+	depth int
+}
+
+func flatten(node *yaml.Node, depth int) {
+	if depth == 0 {
+		return
+	}
+	if node.Kind != yaml.SequenceNode {
+		return
+	}
+	content := node.Content
+	newSeq := make([]*yaml.Node, 0)
+
+	for i := 0; i < len(content); i++ {
+		if content[i].Kind == yaml.SequenceNode {
+			flatten(content[i], depth-1)
+			for j := 0; j < len(content[i].Content); j++ {
+				newSeq = append(newSeq, content[i].Content[j])
+			}
+		} else {
+			newSeq = append(newSeq, content[i])
+		}
+	}
+	node.Content = newSeq
+}
+
+func flattenOp(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
+
+	log.Debugf("-- flatten Operator")
+	depth := expressionNode.Operation.Preferences.(flattenPreferences).depth
+
+	for el := context.MatchingNodes.Front(); el != nil; el = el.Next() {
+		candidate := el.Value.(*CandidateNode)
+		candidateNode := unwrapDoc(candidate.Node)
+		if candidateNode.Kind != yaml.SequenceNode {
+			return Context{}, fmt.Errorf("Only arrays are supported for group by")
+		}
+
+		flatten(candidateNode, depth)
+
+	}
+
+	return context, nil
+
+}