Add pivot and unpivot processors (#5991)

plugins/processors/pivot/README.md

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+# Pivot Processor
+
+You can use the `pivot` processor to rotate single valued metrics into a multi
+field metric.  This transformation often results in data that is more easily
+to apply mathematical operators and comparisons between, and flatten into a
+more compact representation for write operations with some output data
+formats.
+
+To perform the reverse operation use the [unpivot] processor.
+
+### Configuration
+
+```toml
+[[processors.pivot]]
+  ## Tag to use for naming the new field.
+  tag_key = "name"
+  ## Field to use as the value of the new field.
+  value_key = "value"
+```
+
+### Example
+
+```diff
+- cpu,cpu=cpu0,name=time_idle value=42i
+- cpu,cpu=cpu0,name=time_user value=43i
++ cpu,cpu=cpu0 time_idle=42i
++ cpu,cpu=cpu0 time_user=42i
+```
+
+[unpivot]: /plugins/processors/unpivot/README.md

plugins/processors/pivot/pivot.go

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+package pivot
+
+import (
+	"github.com/influxdata/telegraf"
+	"github.com/influxdata/telegraf/plugins/processors"
+)
+
+const (
+	description  = "Rotate a single valued metric into a multi field metric"
+	sampleConfig = `
+  ## Tag to use for naming the new field.
+  tag_key = "name"
+  ## Field to use as the value of the new field.
+  value_key = "value"
+`
+)
+
+type Pivot struct {
+	TagKey   string `toml:"tag_key"`
+	ValueKey string `toml:"value_key"`
+}
+
+func (p *Pivot) SampleConfig() string {
+	return sampleConfig
+}
+
+func (p *Pivot) Description() string {
+	return description
+}
+
+func (p *Pivot) Apply(metrics ...telegraf.Metric) []telegraf.Metric {
+	for _, m := range metrics {
+		key, ok := m.GetTag(p.TagKey)
+		if !ok {
+			continue
+		}
+
+		value, ok := m.GetField(p.ValueKey)
+		if !ok {
+			continue
+		}
+
+		m.RemoveTag(p.TagKey)
+		m.RemoveField(p.ValueKey)
+		m.AddField(key, value)
+	}
+	return metrics
+}
+
+func init() {
+	processors.Add("pivot", func() telegraf.Processor {
+		return &Pivot{}
+	})
+}

plugins/processors/pivot/pivot_test.go

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+package pivot
+
+import (
+	"testing"
+	"time"
+
+	"github.com/influxdata/telegraf"
+	"github.com/influxdata/telegraf/testutil"
+)
+
+func TestPivot(t *testing.T) {
+	now := time.Now()
+	tests := []struct {
+		name     string
+		pivot    *Pivot
+		metrics  []telegraf.Metric
+		expected []telegraf.Metric
+	}{
+		{
+			name: "simple",
+			pivot: &Pivot{
+				TagKey:   "name",
+				ValueKey: "value",
+			},
+			metrics: []telegraf.Metric{
+				testutil.MustMetric("cpu",
+					map[string]string{
+						"name": "idle_time",
+					},
+					map[string]interface{}{
+						"value": int64(42),
+					},
+					now,
+				),
+			},
+			expected: []telegraf.Metric{
+				testutil.MustMetric("cpu",
+					map[string]string{},
+					map[string]interface{}{
+						"idle_time": int64(42),
+					},
+					now,
+				),
+			},
+		},
+		{
+			name: "missing tag",
+			pivot: &Pivot{
+				TagKey:   "name",
+				ValueKey: "value",
+			},
+			metrics: []telegraf.Metric{
+				testutil.MustMetric("cpu",
+					map[string]string{
+						"foo": "idle_time",
+					},
+					map[string]interface{}{
+						"value": int64(42),
+					},
+					now,
+				),
+			},
+			expected: []telegraf.Metric{
+				testutil.MustMetric("cpu",
+					map[string]string{
+						"foo": "idle_time",
+					},
+					map[string]interface{}{
+						"value": int64(42),
+					},
+					now,
+				),
+			},
+		},
+		{
+			name: "missing field",
+			pivot: &Pivot{
+				TagKey:   "name",
+				ValueKey: "value",
+			},
+			metrics: []telegraf.Metric{
+				testutil.MustMetric("cpu",
+					map[string]string{
+						"name": "idle_time",
+					},
+					map[string]interface{}{
+						"foo": int64(42),
+					},
+					now,
+				),
+			},
+			expected: []telegraf.Metric{
+				testutil.MustMetric("cpu",
+					map[string]string{
+						"name": "idle_time",
+					},
+					map[string]interface{}{
+						"foo": int64(42),
+					},
+					now,
+				),
+			},
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			actual := tt.pivot.Apply(tt.metrics...)
+			testutil.RequireMetricsEqual(t, tt.expected, actual)
+		})
+	}
+}