Added unique operator

pkg/yqlib/operator_unique.go

@@ -0,0 +1,59 @@
+package yqlib
+
+import (
+	"github.com/elliotchance/orderedmap"
+	"container/list"
+	yaml "gopkg.in/yaml.v3"
+	"fmt"
+)
+
+func unique(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
+	selfExpression := &ExpressionNode{Operation: &Operation{OperationType: selfReferenceOpType}}
+	uniqueByExpression := &ExpressionNode{Operation: &Operation{OperationType: uniqueByOpType}, Rhs: selfExpression}
+	return uniqueBy(d, context, uniqueByExpression)
+
+}
+
+func uniqueBy(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
+
+	log.Debugf("-- uniqueBy Operator")
+	var results = list.New()
+
+
+	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 unique")
+		}
+		
+		var newMatches = orderedmap.NewOrderedMap()
+		for _, node := range candidateNode.Content {
+			child := &CandidateNode{Node: node}
+			rhs, err := d.GetMatchingNodes(context.SingleChildContext(child), expressionNode.Rhs)
+
+			if err != nil {
+				return Context{}, err
+			}
+
+			first := rhs.MatchingNodes.Front()
+			keyCandidate := first.Value.(*CandidateNode)
+			keyValue := keyCandidate.Node.Value
+			_, exists := newMatches.Get(keyValue)
+
+			if !exists {
+				newMatches.Set(keyValue, child.Node)
+			}
+		}
+		resultNode := &yaml.Node{Kind: yaml.SequenceNode, Tag: "!!seq"}
+		for el := newMatches.Front(); el != nil; el = el.Next() {
+			resultNode.Content = append(resultNode.Content, el.Value.(*yaml.Node))
+		}
+
+		results.PushBack(candidate.CreateChild(nil, resultNode))
+	}
+
+	return context.ChildContext(results), nil
+
+}