io.trino.operator.scalar.ArrayShuffleFunction Maven / Gradle / Ivy
/*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package io.trino.operator.scalar;
import io.trino.spi.block.Block;
import io.trino.spi.block.BufferedArrayValueBuilder;
import io.trino.spi.function.Description;
import io.trino.spi.function.ScalarFunction;
import io.trino.spi.function.SqlType;
import io.trino.spi.function.TypeParameter;
import io.trino.spi.type.ArrayType;
import io.trino.spi.type.Type;
import java.util.concurrent.ThreadLocalRandom;
@ScalarFunction(value = "shuffle", deterministic = false)
@Description("Generates a random permutation of the given array.")
public final class ArrayShuffleFunction
{
private final BufferedArrayValueBuilder arrayValueBuilder;
private static final int INITIAL_LENGTH = 128;
private int[] positions = new int[INITIAL_LENGTH];
@TypeParameter("E")
public ArrayShuffleFunction(@TypeParameter("E") Type elementType)
{
arrayValueBuilder = BufferedArrayValueBuilder.createBuffered(new ArrayType(elementType));
}
@TypeParameter("E")
@SqlType("array(E)")
public Block shuffle(
@TypeParameter("E") Type type,
@SqlType("array(E)") Block block)
{
int length = block.getPositionCount();
if (positions.length < length) {
positions = new int[length];
}
for (int i = 0; i < length; i++) {
positions[i] = i;
}
// Fisher-Yates shuffle
// Randomly swap a pair of positions
for (int i = length - 1; i > 0; i--) {
int index = ThreadLocalRandom.current().nextInt(i + 1);
int swap = positions[i];
positions[i] = positions[index];
positions[index] = swap;
}
return arrayValueBuilder.build(length, elementBuilder -> {
for (int i = 0; i < length; i++) {
type.appendTo(block, positions[i], elementBuilder);
}
});
}
}