Add date related functions.

Add day_of_month, day_of_week, hour_of_day, month_of_year and year.
This only work for UTC, and ignore leap seconds the same as Go.

promql/functions.go

@@ -18,6 +18,7 @@ import (
 	"regexp"
 	"sort"
 	"strconv"
+	"time"
 
 	"github.com/prometheus/common/model"
 
@@ -859,6 +860,57 @@ func funcVector(ev *evaluator, args Expressions) model.Value {
 	}
 }
 
+// === day_of_month(v vector) scalar ===
+func funcDayOfMonth(ev *evaluator, args Expressions) model.Value {
+	vector := ev.evalVector(args[0])
+	for _, el := range vector {
+		el.Metric.Del(model.MetricNameLabel)
+		el.Value = model.SampleValue(time.Unix(int64(el.Value), 0).UTC().Day())
+	}
+	return vector
+}
+
+// === day_of_week(v vector) scalar ===
+func funcDayOfWeek(ev *evaluator, args Expressions) model.Value {
+	vector := ev.evalVector(args[0])
+	for _, el := range vector {
+		el.Metric.Del(model.MetricNameLabel)
+		// Sunday = 0.
+		el.Value = model.SampleValue(time.Unix(int64(el.Value), 0).UTC().Weekday())
+	}
+	return vector
+}
+
+// === hour_of_day(v vector) scalar ===
+func funcHourOfDay(ev *evaluator, args Expressions) model.Value {
+	vector := ev.evalVector(args[0])
+	for _, el := range vector {
+		el.Metric.Del(model.MetricNameLabel)
+		el.Value = model.SampleValue(time.Unix(int64(el.Value), 0).UTC().Hour())
+	}
+	return vector
+}
+
+// === month_of_year(v vector) scalar ===
+func funcMonthOfYear(ev *evaluator, args Expressions) model.Value {
+	vector := ev.evalVector(args[0])
+	for _, el := range vector {
+		el.Metric.Del(model.MetricNameLabel)
+		el.Value = model.SampleValue(time.Unix(int64(el.Value), 0).UTC().Month())
+	}
+	return vector
+}
+
+// === year(v vector) scalar ===
+func funcYear(ev *evaluator, args Expressions) model.Value {
+	vector := ev.evalVector(args[0])
+	for _, el := range vector {
+		el.Metric.Del(model.MetricNameLabel)
+		el.Value = model.SampleValue(time.Unix(int64(el.Value), 0).UTC().Year())
+	}
+	return vector
+}
+
 var functions = map[string]*Function{
 	"abs": {
 		Name:       "abs",
@@ -920,6 +972,18 @@ var functions = map[string]*Function{
 		ReturnType: model.ValScalar,
 		Call:       funcCountScalar,
 	},
+	"day_of_month": {
+		Name:       "day_of_month",
+		ArgTypes:   []model.ValueType{model.ValVector},
+		ReturnType: model.ValVector,
+		Call:       funcDayOfMonth,
+	},
+	"day_of_week": {
+		Name:       "day_of_week",
+		ArgTypes:   []model.ValueType{model.ValVector},
+		ReturnType: model.ValVector,
+		Call:       funcDayOfWeek,
+	},
 	"delta": {
 		Name:       "delta",
 		ArgTypes:   []model.ValueType{model.ValMatrix},
@@ -962,6 +1026,12 @@ var functions = map[string]*Function{
 		ReturnType: model.ValVector,
 		Call:       funcHoltWinters,
 	},
+	"hour_of_day": {
+		Name:       "hour_of_day",
+		ArgTypes:   []model.ValueType{model.ValVector},
+		ReturnType: model.ValVector,
+		Call:       funcHourOfDay,
+	},
 	"irate": {
 		Name:       "irate",
 		ArgTypes:   []model.ValueType{model.ValMatrix},
@@ -1010,6 +1080,12 @@ var functions = map[string]*Function{
 		ReturnType: model.ValVector,
 		Call:       funcMinOverTime,
 	},
+	"month_of_year": {
+		Name:       "month_of_year",
+		ArgTypes:   []model.ValueType{model.ValVector},
+		ReturnType: model.ValVector,
+		Call:       funcMonthOfYear,
+	},
 	"predict_linear": {
 		Name:       "predict_linear",
 		ArgTypes:   []model.ValueType{model.ValMatrix, model.ValScalar},
@@ -1095,6 +1171,12 @@ var functions = map[string]*Function{
 		ReturnType: model.ValVector,
 		Call:       funcVector,
 	},
+	"year": {
+		Name:       "year",
+		ArgTypes:   []model.ValueType{model.ValVector},
+		ReturnType: model.ValVector,
+		Call:       funcYear,
+	},
 }
 
 // getFunction returns a predefined Function object for the given name.

promql/testdata/functions.test

@@ -363,3 +363,38 @@ eval instant at 1m quantile_over_time(2, data[1m])
 	{test="two samples"} +Inf
 	{test="three samples"} +Inf
 	{test="uneven samples"} +Inf
+
+clear
+
+# Test time-related functions.
+eval instant at 0m year(vector(0))
+  {} 1970
+
+eval instant at 0m month_of_year(vector(0))
+  {} 1
+
+eval instant at 0m day_of_month(vector(0))
+  {} 1
+
+# Thursday.
+eval instant at 0m day_of_week(vector(0))
+  {} 4
+
+eval instant at 0m hour_of_day(vector(0))
+  {} 0
+
+# 2008-12-31 23:59:59 just before leap second.
+eval instant at 0m year(vector(1230767999))
+  {} 2008
+
+# 2009-01-01 00:00:00 just after leap second.
+eval instant at 0m year(vector(1230768000))
+  {} 2009
+
+# 2016-02-29 23:59:59 Febuary 29th in leap year.
+eval instant at 0m month_of_year(vector(1456790399)) + day_of_month(vector(1456790399)) / 100
+  {} 2.29
+
+# 2016-03-01 00:00:00 March 1st in leap year.
+eval instant at 0m month_of_year(vector(1456790400)) + day_of_month(vector(1456790400)) / 100
+  {} 3.01