Make DefaultMedian faster

gselzer · elevans · commit d9ff43cd7b3e · 2025-02-14T14:38:51.000-06:00
diff --git a/scijava-ops-image/src/main/java/org/scijava/ops/image/stats/DefaultMedian.java b/scijava-ops-image/src/main/java/org/scijava/ops/image/stats/DefaultMedian.java
@@ -29,12 +29,10 @@
 
 package org.scijava.ops.image.stats;
 
-import java.util.ArrayList;
-
 import net.imglib2.type.numeric.RealType;
 
+import org.scijava.collections.DoubleArray;
 import org.scijava.function.Computers;
-import org.scijava.ops.spi.Op;
 import org.scijava.ops.spi.OpDependency;
 
 /**
@@ -55,6 +53,11 @@ public class DefaultMedian<I extends RealType<I>, O extends RealType<O>>
 	@OpDependency(name = "stats.quantile")
 	private Computers.Arity2<Iterable<I>, Double, O> quantileOp;
 
+	/**
+	 * TODO: One/many of these lists could get really big over time. Maybe that will be a problem?
+	 */
+	private static final ThreadLocal<DoubleArray> BUFFER = ThreadLocal.withInitial(DoubleArray::new);
+
 	/**
 	 * TODO
 	 *
@@ -63,9 +66,11 @@ public class DefaultMedian<I extends RealType<I>, O extends RealType<O>>
 	 */
 	@Override
 	public void compute(final Iterable<I> input, final O median) {
-		final var statistics = new ArrayList<Double>();
+		final var statistics = BUFFER.get();
+		statistics.clear();
+//		final var statistics = new ArrayList<Double>();
 
-		input.forEach(i -> statistics.add(i.getRealDouble()));
+		input.forEach(i -> statistics.addValue(i.getRealDouble()));
 
 		final var k = statistics.size() / 2;
         var result = DefaultQuantile.select(statistics, k);
diff --git a/scijava-ops-image/src/main/java/org/scijava/ops/image/stats/DefaultQuantile.java b/scijava-ops-image/src/main/java/org/scijava/ops/image/stats/DefaultQuantile.java
@@ -33,6 +33,7 @@
 import org.scijava.function.Computers;
 
 import java.util.ArrayList;
+import java.util.List;
 
 import static java.util.Collections.swap;
 
@@ -83,7 +84,7 @@ public void compute(final Iterable<I> input, final N quantile,
 	 * This an all-in-one method version of your basic quick select algorithm.
 	 * </p>
 	 */
-	static double select(final ArrayList<Double> array, final int k) {
+	static double select(final List<Double> array, final int k) {
 
         var left = 0;
         var right = array.size() - 1;
