Github user thunterdb commented on a diff in the pull request: https://github.com/apache/spark/pull/19439#discussion_r150247999 --- Diff: mllib/src/main/scala/org/apache/spark/ml/image/HadoopUtils.scala --- @@ -0,0 +1,109 @@ +/* + * Licensed to the Apache Software Foundation (ASF) under one or more + * contributor license agreements. See the NOTICE file distributed with + * this work for additional information regarding copyright ownership. + * The ASF licenses this file to You 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 org.apache.spark.ml.image + +import scala.language.existentials +import scala.util.Random + +import org.apache.commons.io.FilenameUtils +import org.apache.hadoop.conf.{Configuration, Configured} +import org.apache.hadoop.fs.{Path, PathFilter} +import org.apache.hadoop.mapreduce.lib.input.FileInputFormat + +import org.apache.spark.sql.SparkSession + +private object RecursiveFlag { + /** + * Sets the spark recursive flag and then restores it. + * + * @param value Value to set + * @param spark Existing spark session + * @param f The function to evaluate after setting the flag + * @return Returns the evaluation result T of the function + */ + def withRecursiveFlag[T](value: Boolean, spark: SparkSession)(f: => T): T = { + val flagName = FileInputFormat.INPUT_DIR_RECURSIVE + val hadoopConf = spark.sparkContext.hadoopConfiguration + val old = Option(hadoopConf.get(flagName)) + hadoopConf.set(flagName, value.toString) + try f finally { + old match { + case Some(v) => hadoopConf.set(flagName, v) + case None => hadoopConf.unset(flagName) + } + } + } +} + +/** + * Filter that allows loading a fraction of HDFS files. + */ +private class SamplePathFilter extends Configured with PathFilter { --- End diff -- Oh, it would be pretty simple to work it out this way (pseudocode). Note that a hash is a random variable between -2^31 and 2^31-1, so: ``` val fraction: Double = ??? // Something between 0 and 1 val pathname: String = ??? val hash = pathname.hashcode() // Could use some other other, more robust methods that return longs. val shouldKeep: Boolean = math.abs(hash) < (math.pow(2, 31) * fraction) ```
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