min/max operators (#1992)

* min/max operators

* min, max operator headers

pkg/yqlib/doc/operators/headers/max.md

@@ -0,0 +1,3 @@
+# Max
+
+Computes the maximum among an incoming sequence of scalar values.

pkg/yqlib/doc/operators/headers/min.md

@@ -0,0 +1,3 @@
+# Min
+
+Computes the minimum among an incoming sequence of scalar values.

pkg/yqlib/doc/operators/max.md

@@ -0,0 +1,48 @@
+
+## Maximum int
+Given a sample.yml file of:
+```yaml
+- 99
+- 16
+- 12
+- 6
+- 66
+```
+then
+```bash
+yq 'max' sample.yml
+```
+will output
+```yaml
+99
+```
+
+## Maximum string
+Given a sample.yml file of:
+```yaml
+- foo
+- bar
+- baz
+```
+then
+```bash
+yq 'max' sample.yml
+```
+will output
+```yaml
+foo
+```
+
+## Maximum of empty
+Given a sample.yml file of:
+```yaml
+[]
+```
+then
+```bash
+yq 'max' sample.yml
+```
+will output
+```yaml
+```
+

pkg/yqlib/doc/operators/min.md

@@ -0,0 +1,48 @@
+
+## Minimum int
+Given a sample.yml file of:
+```yaml
+- 99
+- 16
+- 12
+- 6
+- 66
+```
+then
+```bash
+yq 'min' sample.yml
+```
+will output
+```yaml
+6
+```
+
+## Minimum string
+Given a sample.yml file of:
+```yaml
+- foo
+- bar
+- baz
+```
+then
+```bash
+yq 'min' sample.yml
+```
+will output
+```yaml
+bar
+```
+
+## Minimum of empty
+Given a sample.yml file of:
+```yaml
+[]
+```
+then
+```bash
+yq 'min' sample.yml
+```
+will output
+```yaml
+```
+

pkg/yqlib/lexer_participle.go

@@ -199,6 +199,9 @@ var participleYqRules = []*participleYqRule{
 	{"GreaterThan", `\s*>\s*`, opTokenWithPrefs(compareOpType, nil, compareTypePref{OrEqual: false, Greater: true}), 0},
 	{"LessThan", `\s*<\s*`, opTokenWithPrefs(compareOpType, nil, compareTypePref{OrEqual: false, Greater: false}), 0},
 
+	simpleOp("min", minOpType),
+	simpleOp("max", maxOpType),
+
 	{"AssignRelative", `\|=[c]*`, assignOpToken(true), 0},
 	{"Assign", `=[c]*`, assignOpToken(false), 0},
 

pkg/yqlib/operation.go

@@ -73,6 +73,8 @@ var equalsOpType = &operationType{Type: "EQUALS", NumArgs: 2, Precedence: 40, Ha
 var notEqualsOpType = &operationType{Type: "NOT_EQUALS", NumArgs: 2, Precedence: 40, Handler: notEqualsOperator}
 
 var compareOpType = &operationType{Type: "COMPARE", NumArgs: 2, Precedence: 40, Handler: compareOperator}
+var minOpType = &operationType{Type: "MIN", NumArgs: 0, Precedence: 40, Handler: minOperator}
+var maxOpType = &operationType{Type: "MAX", NumArgs: 0, Precedence: 40, Handler: maxOperator}
 
 // createmap needs to be above union, as we use union to build the components of the objects
 var createMapOpType = &operationType{Type: "CREATE_MAP", NumArgs: 2, Precedence: 15, Handler: createMapOperator}

pkg/yqlib/operator_compare.go

@@ -1,6 +1,7 @@
 package yqlib
 
 import (
+	"container/list"
 	"fmt"
 	"strconv"
 )
@@ -129,3 +130,40 @@ func compareScalars(context Context, prefs compareTypePref, lhs *CandidateNode,
 
 	return false, fmt.Errorf("%v not yet supported for comparison", lhs.Tag)
 }
+
+func superlativeByComparison(d *dataTreeNavigator, context Context, prefs compareTypePref) (Context, error) {
+	fn := compare(prefs)
+
+	var results = list.New()
+
+	for seq := context.MatchingNodes.Front(); seq != nil; seq = seq.Next() {
+		splatted, err := splat(context.SingleChildContext(seq.Value.(*CandidateNode)), traversePreferences{})
+		if err != nil {
+			return Context{}, err
+		}
+		result := splatted.MatchingNodes.Front()
+		if result != nil {
+			for el := result.Next(); el != nil; el = el.Next() {
+				cmp, err := fn(d, context, el.Value.(*CandidateNode), result.Value.(*CandidateNode))
+				if err != nil {
+					return Context{}, err
+				}
+				if isTruthyNode(cmp) {
+					result = el
+				}
+			}
+			results.PushBack(result.Value)
+		}
+	}
+	return context.ChildContext(results), nil
+}
+
+func minOperator(d *dataTreeNavigator, context Context, _ *ExpressionNode) (Context, error) {
+	log.Debug(("Min"))
+	return superlativeByComparison(d, context, compareTypePref{Greater: false})
+}
+
+func maxOperator(d *dataTreeNavigator, context Context, _ *ExpressionNode) (Context, error) {
+	log.Debug(("Max"))
+	return superlativeByComparison(d, context, compareTypePref{Greater: true})
+}

pkg/yqlib/operators_compare_test.go

@@ -383,3 +383,67 @@ func TestCompareOperatorScenarios(t *testing.T) {
 	}
 	documentOperatorScenarios(t, "compare", compareOperatorScenarios)
 }
+
+var minOperatorScenarios = []expressionScenario{
+	{
+		description: "Minimum int",
+		document:    "[99, 16, 12, 6, 66]\n",
+		expression:  `min`,
+		expected: []string{
+			"D0, P[3], (!!int)::6\n",
+		},
+	},
+	{
+		description: "Minimum string",
+		document:    "[foo, bar, baz]\n",
+		expression:  `min`,
+		expected: []string{
+			"D0, P[1], (!!str)::bar\n",
+		},
+	},
+	{
+		description: "Minimum of empty",
+		document:    "[]\n",
+		expression:  `min`,
+		expected:    []string{},
+	},
+}
+
+func TestMinOperatorScenarios(t *testing.T) {
+	for _, tt := range minOperatorScenarios {
+		testScenario(t, &tt)
+	}
+	documentOperatorScenarios(t, "min", minOperatorScenarios)
+}
+
+var maxOperatorScenarios = []expressionScenario{
+	{
+		description: "Maximum int",
+		document:    "[99, 16, 12, 6, 66]\n",
+		expression:  `max`,
+		expected: []string{
+			"D0, P[0], (!!int)::99\n",
+		},
+	},
+	{
+		description: "Maximum string",
+		document:    "[foo, bar, baz]\n",
+		expression:  `max`,
+		expected: []string{
+			"D0, P[0], (!!str)::foo\n",
+		},
+	},
+	{
+		description: "Maximum of empty",
+		document:    "[]\n",
+		expression:  `max`,
+		expected:    []string{},
+	},
+}
+
+func TestMaxOperatorScenarios(t *testing.T) {
+	for _, tt := range maxOperatorScenarios {
+		testScenario(t, &tt)
+	}
+	documentOperatorScenarios(t, "max", maxOperatorScenarios)
+}