[processor/transform] introduce aggregate_on_attribute_value function…

… for metrics (open-telemetry#33423)

**Link to tracking Issue:** open-telemetry#16224 

**Changes:**

- implemented `aggregate_on_attribute_value` function
- tests
- documentation

**Depends on**
open-telemetry#33669

---------

Signed-off-by: odubajDT <ondrej.dubaj@dynatrace.com>

.chloggen/feat_16224_aggregate_label_value.yaml

@@ -0,0 +1,27 @@
+# Use this changelog template to create an entry for release notes.
+
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: enhancement
+
+# The name of the component, or a single word describing the area of concern, (e.g. filelogreceiver)
+component: transformprocessor
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: "Support aggregating metrics based on their attribute values and substituting the values with a new value."
+
+# Mandatory: One or more tracking issues related to the change. You can use the PR number here if no issue exists.
+issues: [16224]
+
+# (Optional) One or more lines of additional information to render under the primary note.
+# These lines will be padded with 2 spaces and then inserted directly into the document.
+# Use pipe (|) for multiline entries.
+subtext:
+
+# If your change doesn't affect end users or the exported elements of any package,
+# you should instead start your pull request title with [chore] or use the "Skip Changelog" label.
+# Optional: The change log or logs in which this entry should be included.
+# e.g. '[user]' or '[user, api]'
+# Include 'user' if the change is relevant to end users.
+# Include 'api' if there is a change to a library API.
+# Default: '[user]'
+change_logs: [user]

processor/transformprocessor/README.md

@@ -220,6 +220,7 @@ In addition to OTTL functions, the processor defines its own functions to help w
 - [copy_metric](#copy_metric)
 - [scale_metric](#scale_metric)
 - [aggregate_on_attributes](#aggregate_on_attributes)
+- [aggregate_on_attribute_value](#aggregate_on_attribute_value)
 
 ### convert_sum_to_gauge
 
@@ -374,10 +375,12 @@ Examples:
 
 `aggregate_on_attributes(function, Optional[attributes])`
 
-The `aggregate_on_attributes` function aggregates all datapoints in the metric based on the supplied attributes. `function` is a case-sensitive string that represents the aggregation function and `attributes` is an optional list of attribute keys to aggregate upon.
+The `aggregate_on_attributes` function aggregates all datapoints in the metric based on the supplied attributes. `function` is a case-sensitive string that represents the aggregation function and `attributes` is an optional list of attribute keys of type string to aggregate upon.
 
 `aggregate_on_attributes` function removes all attributes that are present in datapoints except the ones that are specified in the `attributes` parameter. If `attributes` parameter is not set, all attributes are removed from datapoints. Afterwards all datapoints are aggregated depending on the attributes left (none or the ones present in the list).
 
+**NOTE:** This function is supported only in `metric` context.
+
 The following metric types can be aggregated:
 
 - sum
@@ -415,6 +418,50 @@ statements:
 
 To aggregate only using a specified set of attributes, you can use `keep_matching_keys`.
 
+### aggregate_on_attribute_value
+
+`aggregate_on_attribute_value(function, attribute, values, newValue)`
+
+The `aggregate_on_attribute_value` function aggregates all datapoints in the metric containing the attribute `attribute` (type string) with one of the values present in the `values` parameter (list of strings) into a single datapoint where the attribute has the value `newValue` (type string). `function` is a case-sensitive string that represents the aggregation function.
+
+**NOTE:** This function is supported only in `metric` context.
+
+The following metric types can be aggregated:
+
+- sum
+- gauge
+- histogram
+- exponential histogram
+
+Supported aggregation functions are:
+
+- sum
+- max
+- min
+- mean
+- median
+- count
+
+**NOTE:** Only the `sum` agregation function is supported for histogram and exponential histogram datatypes.
+
+Examples:
+
+- `aggregate_on_attribute_value("sum", "attr1", ["val1", "val2"], "new_val") where name == "system.memory.usage"`
+
+The `aggregate_on_attribute_value` function can also be used in conjunction with 
+[keep_matching_keys](https://github.com/open-telemetry/opentelemetry-collector-contrib/blob/main/pkg/ottl/ottlfuncs#keep_matching_keys) or
+[delete_matching_keys](https://github.com/open-telemetry/opentelemetry-collector-contrib/blob/main/pkg/ottl/ottlfuncs#delete_matching_keys).
+
+For example, to remove attribute keys matching a regex and aggregate the metrics on the remaining attributes, you can perform the following statement sequence:
+
+```yaml
+statements:
+   - delete_matching_keys(attributes, "(?i).*myRegex.*") where name == "system.memory.usage"
+   - aggregate_on_attribute_value("sum", "attr1", ["val1", "val2"], "new_val") where name == "system.memory.usage"
+```
+
+To aggregate only using a specified set of attributes, you can use `keep_matching_keys`.
+
 ## Examples
 
 ### Perform transformation if field does not exist

processor/transformprocessor/internal/metrics/func_agregate_on_attribute_value_metrics.go

@@ -0,0 +1,70 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+package metrics // import "github.com/open-telemetry/opentelemetry-collector-contrib/processor/transformprocessor/internal/metrics"
+
+import (
+	"context"
+	"fmt"
+
+	"go.opentelemetry.io/collector/pdata/pcommon"
+	"go.opentelemetry.io/collector/pdata/pmetric"
+
+	"github.com/open-telemetry/opentelemetry-collector-contrib/internal/coreinternal/aggregateutil"
+	"github.com/open-telemetry/opentelemetry-collector-contrib/pkg/ottl"
+	"github.com/open-telemetry/opentelemetry-collector-contrib/pkg/ottl/contexts/ottlmetric"
+)
+
+type aggregateOnAttributeValueArguments struct {
+	AggregationFunction string
+	Attribute           string
+	Values              []string
+	NewValue            string
+}
+
+func newAggregateOnAttributeValueFactory() ottl.Factory[ottlmetric.TransformContext] {
+	return ottl.NewFactory("aggregate_on_attribute_value", &aggregateOnAttributeValueArguments{}, createAggregateOnAttributeValueFunction)
+}
+
+func createAggregateOnAttributeValueFunction(_ ottl.FunctionContext, oArgs ottl.Arguments) (ottl.ExprFunc[ottlmetric.TransformContext], error) {
+	args, ok := oArgs.(*aggregateOnAttributeValueArguments)
+
+	if !ok {
+		return nil, fmt.Errorf("AggregateOnAttributeValueFactory args must be of type *AggregateOnAttributeValueArguments")
+	}
+
+	t, err := aggregateutil.ConvertToAggregationFunction(args.AggregationFunction)
+	if err != nil {
+		return nil, fmt.Errorf("invalid aggregation function: '%s', valid options: %s", err.Error(), aggregateutil.GetSupportedAggregationFunctionsList())
+	}
+
+	return AggregateOnAttributeValue(t, args.Attribute, args.Values, args.NewValue)
+}
+
+func AggregateOnAttributeValue(aggregationType aggregateutil.AggregationType, attribute string, values []string, newValue string) (ottl.ExprFunc[ottlmetric.TransformContext], error) {
+	return func(_ context.Context, tCtx ottlmetric.TransformContext) (any, error) {
+		metric := tCtx.GetMetric()
+
+		aggregateutil.RangeDataPointAttributes(metric, func(attrs pcommon.Map) bool {
+			val, ok := attrs.Get(attribute)
+			if !ok {
+				return true
+			}
+
+			for _, v := range values {
+				if val.Str() == v {
+					val.SetStr(newValue)
+				}
+			}
+			return true
+		})
+		ag := aggregateutil.AggGroups{}
+		newMetric := pmetric.NewMetric()
+		aggregateutil.CopyMetricDetails(metric, newMetric)
+		aggregateutil.GroupDataPoints(metric, &ag)
+		aggregateutil.MergeDataPoints(newMetric, aggregationType, ag)
+		newMetric.MoveTo(metric)
+
+		return nil, nil
+	}, nil
+}