diff --git a/list-type.go b/list-type.go
index eddf8cd..b2442c1 100644
--- a/list-type.go
+++ b/list-type.go
@@ -134,7 +134,7 @@ func (ls1 *ListType) Equals(ls2 ListType) (answer bool) {
 		answer = true
 		for index, i1 := range *ls1 {
 			// if i1 != (ls2)[index] {
-			if reflect.DeepEqual(i1, ls2[index]) {
+			if !reflect.DeepEqual(i1, ls2[index]) {
 				answer = false
 				break
 			}
diff --git a/operator-filter.go b/operator-filter.go
new file mode 100644
index 0000000..459041f
--- /dev/null
+++ b/operator-filter.go
@@ -0,0 +1,70 @@
+// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
+// All rights reserved.
+
+// operator-filter.go
+package expr
+
+import (
+	"fmt"
+	"io"
+)
+
+//-------- map term
+
+func newFilterTerm(tk *Token) (inst *term) {
+	return &term{
+		tk:       *tk,
+		children: make([]*term, 0, 2),
+		position: posInfix,
+		priority: priIterOp,
+		evalFunc: evalFilter,
+	}
+}
+
+func evalFilter(ctx ExprContext, opTerm *term) (v any, err error) {
+	var leftValue, rightValue any
+	var it Iterator
+	var item any
+
+	if err = opTerm.checkOperands(); err != nil {
+		return
+	}
+
+	if leftValue, err = opTerm.children[0].compute(ctx); err != nil {
+		return
+	}
+
+	if it, err = NewIterator(leftValue); err != nil {
+		return nil, fmt.Errorf("left operand of MAP must be an iterable data-source; got %s", TypeName(leftValue))
+	}
+
+	values := newListA()
+	for item, err = it.Next(); err == nil; item, err = it.Next() {
+		ctx.SetVar("_", item)
+		ctx.SetVar("_index", it.Index())
+		ctx.SetVar("_count", it.Count())
+		if rightValue, err = opTerm.children[1].compute(ctx); err == nil {
+			if success, valid := ToBool(rightValue); valid {
+				if success {
+					values.appendItem(item)
+				}
+			} else {
+				err = fmt.Errorf("filter expression must return a boolean or a castable to boolean, got %v [%T]", rightValue, rightValue)
+			}
+		}
+		ctx.DeleteVar("_")
+		if err != nil {
+			break
+		}
+	}
+	if err == io.EOF {
+		err = nil
+	}
+	v = values
+	return
+}
+
+// init
+func init() {
+	registerTermConstructor(SymKwFilter, newFilterTerm)
+}
diff --git a/symbol-map.go b/symbol-map.go
index 9e0e3c7..a5b175c 100644
--- a/symbol-map.go
+++ b/symbol-map.go
@@ -131,10 +131,13 @@ func init() {
 		// // SymClosedComment                     //   0: '*/'
 		// // SymOneLineComment                    //   0: '//'
 		// keywordBase
-		SymKwAnd:     {"and", symClassOperator, posInfix},
-		SymKwNot:     {"not", symClassOperator, posInfix},
-		SymKwOr:      {"or", symClassOperator, posInfix},
-		SymKwBut:     {"but", symClassOperator, posInfix},
+		SymKwAnd:    {"and", symClassOperator, posInfix},
+		SymKwNot:    {"not", symClassOperator, posInfix},
+		SymKwOr:     {"or", symClassOperator, posInfix},
+		SymKwBut:    {"but", symClassOperator, posInfix},
+		SymKwMap:    {"map", symClassOperator, posInfix},
+		SymKwFilter: {"filter", symClassOperator, posInfix},
+		// SymKwDigest:  {"digest", symClassOperator, posInfix},
 		SymKwFunc:    {"func(", symClassDeclaration, posPrefix},
 		SymKwBuiltin: {"builtin", symClassOperator, posPrefix},
 		SymKwPlugin:  {"plugin", symClassOperator, posPrefix},
diff --git a/symbol.go b/symbol.go
index 3c6788e..a395136 100644
--- a/symbol.go
+++ b/symbol.go
@@ -120,6 +120,8 @@ const (
 	SymKwIn
 	SymKwInclude
 	SymKwMap
+	SymKwFilter
+	// SymKwDigest
 	SymKwNil
 	SymKwUnset
 )
@@ -137,9 +139,11 @@ func init() {
 		"IN":      SymKwIn,
 		"INCLUDE": SymKwInclude,
 		"MAP":     SymKwMap,
+		"FILTER":  SymKwFilter,
 		"NOT":     SymKwNot,
 		"OR":      SymKwOr,
 		"NIL":     SymKwNil,
 		"UNSET":   SymKwUnset,
+		// "DIGEST": SymKwDigest,
 	}
 }
diff --git a/t_iterator_test.go b/t_iterator_test.go
index 2bb78c2..9857aa9 100644
--- a/t_iterator_test.go
+++ b/t_iterator_test.go
@@ -32,8 +32,10 @@ func TestIteratorParser(t *testing.T) {
 		/*  21 */ {`it=$({1:"one",2:"two",3:"three"}, "desc", "key"); it++`, int64(3), nil},
 		/*  22 */ {`it=$({1:"one",2:"two",3:"three"}, "asc", "item"); it++`, NewList([]any{int64(1), "one"}), nil},
 		/*  23 */ {`builtin "os.file"; fileReadIterator("test-file.txt") map ${_index}`, NewList([]any{int64(0), int64(1)}), nil},
+		/*  24 */ {`builtin "os.file"; #(fileReadIterator("test-file.txt") filter (#${_} == 2))`, int64(0), nil},
+		/*  25 */ {`builtin "os.file"; #(fileReadIterator("test-file.txt") filter (#${_} == 3))`, int64(2), nil},
 	}
 
-	runTestSuiteSpec(t, section, inputs, 23)
-	// runTestSuite(t, section, inputs)
+	// runTestSuiteSpec(t, section, inputs, 23)
+	runTestSuite(t, section, inputs)
 }
diff --git a/t_operator_test.go b/t_operator_test.go
index cf9afc5..a06c4d5 100644
--- a/t_operator_test.go
+++ b/t_operator_test.go
@@ -33,12 +33,13 @@ func TestOperator(t *testing.T) {
 		/*  20 */ {`a=1; a^=2`, int64(3), nil},
 		/*  21 */ {`a=1; ++a`, int64(2), nil},
 		/*  22 */ {`a=1; --a`, int64(0), nil},
-		/*  23 */ {`[1,2,3] map var("_")`, []any{1, 2, 3}, nil},
-		/*  24 */ {`[1,2,3] map $_`, newList([]any{1, 2, 3}), nil},
+		/*  23 */ {`[1,2,3] map var("_")`, newList([]any{int64(1), int64(2), int64(3)}), nil},
+		/*  24 */ {`[1,2,3] map $_`, newList([]any{int64(1), int64(2), int64(3)}), nil},
+		/*  25 */ {`[1,2,3,4] filter ($_ % 2 == 0)`, newList([]any{int64(2), int64(4)}), nil},
 	}
 
 	// t.Setenv("EXPR_PATH", ".")
 
-	runTestSuiteSpec(t, section, inputs, 24)
-	// runTestSuite(t, section, inputs)
+	// runTestSuiteSpec(t, section, inputs, 25)
+	runTestSuite(t, section, inputs)
 }