Introduce removeIf method to StatefulMetric

prometheus-metrics-core/src/main/java/io/prometheus/metrics/core/metrics/StatefulMetric.java

@@ -10,6 +10,7 @@
 import io.prometheus.metrics.model.snapshots.MetricSnapshot;
 import java.util.ArrayList;
 import java.util.Arrays;
+import java.util.Collections;
 import java.util.List;
 import java.util.Map;
 import java.util.concurrent.ConcurrentHashMap;
@@ -136,6 +137,11 @@ public void remove(String... labelValues) {
     data.remove(Arrays.asList(labelValues));
   }
 
+  /** Remove the data points when the given function. */
+  public void removeIf(Function<List<String>, Boolean> f) {
+    data.entrySet().removeIf(entry -> f.apply(Collections.unmodifiableList(entry.getKey())));
+  }
+
   /** Reset the metric (remove all data points). */
   public void clear() {
     data.clear();

prometheus-metrics-core/src/test/java/io/prometheus/metrics/core/metrics/StatefulMetricTest.java

@@ -4,6 +4,8 @@
 import static org.assertj.core.api.Assertions.assertThatExceptionOfType;
 
 import java.lang.reflect.Field;
+import java.util.Arrays;
+import java.util.List;
 import java.util.Map;
 import org.junit.jupiter.api.Test;
 
@@ -35,6 +37,29 @@ public void testLabelRemoveWhileCollecting() throws Exception {
     }
   }
 
+  @Test
+  @SuppressWarnings("unchecked")
+  public void testLabelRemoveIf() throws Exception {
+    Counter counter =
+        Counter.builder().name("testLabelRemoveIf").labelNames("label1", "label2").build();
+    Field data = counter.getClass().getSuperclass().getDeclaredField("data");
+    data.setAccessible(true);
+
+    counter.labelValues("a", "b").inc(1.0);
+    counter.labelValues("a", "c").inc(3.0);
+    counter.labelValues("a", "d").inc(7.0);
+    counter.labelValues("e", "f").inc(8.0);
+
+    counter.removeIf(labels -> labels.size() == 2 && labels.get(0).equals("a"));
+
+    Map<List<String>, Counter.DataPoint> dataPoints =
+        (Map<List<String>, Counter.DataPoint>) data.get(counter);
+
+    assertThat(dataPoints).hasSize(1);
+    assertThat(dataPoints.get(Arrays.asList("e", "f"))).isNotNull();
+    assertThat(dataPoints.get(Arrays.asList("e", "f")).get()).isEqualTo(8.0D);
+  }
+
   @Test
   public void testClear() {
     Counter counter = Counter.builder().name("test").labelNames("label1", "label2").build();