shuffle | 易学教程

Simple method to shuffle the elements of an array in BASH shell?

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问题 I can do this in PHP but am trying to work within the BASH shell. I need to take an array and then randomly shuffle the contents and dump that to somefile.txt . So given array Heresmyarray, of elements a;b;c;d;e;f; it would produce an output file, output.txt , which would contain elements f;c;b;a;e;d; The elements need to retain the semicolon delimiter. I've seen a number of bash shell array operations but nothing that seems even close to this simple concept. Thanks for any help or

Random Number but Don't Repeat

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问题 I would like to generate a random number less than 50, but once that number has been generated I would like it so that it cannot be generated again. Thanks for the help! 回答1: Please see: Fisher–Yates shuffle: public static void shuffle (int[] array) { Random rng = new Random(); // i.e., java.util.Random. int n = array.length; // The number of items left to shuffle (loop invariant). while (n > 1) { n--; // n is now the last pertinent index int k = rng.nextInt(n + 1); // 0 <= k <= n. int tmp =

Shuffle an array with python, randomize array item order with python

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问题 What's the easiest way to shuffle an array with python? 回答1: import random random.shuffle(array) 回答2: import random random.shuffle(array) 回答3: Alternative way to do this using sklearn from sklearn.utils import shuffle X=[1,2,3] y = ['one', 'two', 'three'] X, y = shuffle(X, y, random_state=0) print(X) print(y) Output: [2, 1, 3] ['two', 'one', 'three'] Advantage: You can random multiple arrays simultaneously without disrupting the mapping. And 'random_state' can control the shuffling for

Shuffle an array with python, randomize array item order with python

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Shuffle list, ensuring that no item remains in same position

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问题 I want to shuffle a list of unique items, but not do an entirely random shuffle. I need to be sure that no element in the shuffled list is at the same position as in the original list. Thus, if the original list is (A, B, C, D, E), this result would be OK: (C, D, B, E, A), but this one would not: (C, E, A, D, B) because "D" is still the fourth item. The list will have at most seven items. Extreme efficiency is not a consideration. I think this modification to Fisher/Yates does the trick, but

What is the purpose of shuffling and sorting phase in the reducer in Map Reduce Programming?

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问题 In Map Reduce programming the reduce phase has shuffling, sorting and reduce as its sub-parts. Sorting is a costly affair. What is the purpose of shuffling and sorting phase in the reducer in Map Reduce Programming? 回答1: First of all shuffling is the process of transfering data from the mappers to the reducers, so I think it is obvious that it is necessary for the reducers, since otherwise, they wouldn't be able to have any input (or input from every mapper). Shuffling can start even before

How can I shuffle the lines of a text file on the Unix command line or in a shell script?

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问题 I want to shuffle the lines of a text file randomly and create a new file. The file may have several thousands of lines. How can I do that with cat , awk , cut , etc? 回答1: You can use shuf. On some systems at least (doesn't appear to be in POSIX). As jleedev pointed out: sort -R might also be an option. On some systems at least; well, you get the picture. It has been pointed out that sort -R doesn't really shuffle but instead sort items according to their hash value. [Editor's note: sort -R

spark shuffle详解（hashShuffle和sortShuffle）

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Shuffle简介 Shuffle描述着数据从map task输出到reduce task输入的这段过程。shuffle是连接Map和Reduce之间的桥梁，Map的输出要用到Reduce中必须经过shuffle这个环节，shuffle的性能高低直接影响了整个程序的性能和吞吐量。因为在分布式情况下，reduce task需要跨节点去拉取其它节点上的map task结果。这一过程将会产生网络资源消耗和内存，磁盘IO的消耗。通常shuffle分为两部分：Map阶段的数据准备和Reduce阶段的数据拷贝处理。一般将在map端的Shuffle称之为Shuffle Write，在Reduce端的Shuffle称之为Shuffle Read. Hadoop MapReduce Shuffle Apache Spark 的 Shuffle 过程与 Apache Hadoop 的 Shuffle 过程有着诸多类似，一些概念可直接套用，例如，Shuffle 过程中，提供数据的一端，被称作 Map 端，Map 端每个生成数据的任务称为 Mapper，对应的，接收数据的一端，被称作 Reduce 端，Reduce 端每个拉取数据的任务称为 Reducer，Shuffle 过程本质上都是将 Map 端获得的数据使用分区器进行划分，并将数据发送给对应的 Reducer 的过程。

MapReduce Shuffle 和 Spark Shuffle 区别看这篇

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MapReduce Shuffle 和 Spark Shuffle 区别看这篇即可 Shuffle的本意是洗牌、混洗的意思，把一组有规则的数据尽量打乱成无规则的数据。而在MapReduce中，Shuffle更像是洗牌的逆过程，指的是将map端的无规则输出按指定的规则“打乱”成具有一定规则的数据，以便reduce端接收处理。其在MapReduce中所处的工作阶段是map输出后到reduce接收前，具体可以分为map端和reduce端前后两个部分。在shuffle之前，也就是在map阶段，MapReduce会对要处理的数据进行分片（split）操作，为每一个分片分配一个MapTask任务。接下来map会对每一个分片中的每一行数据进行处理得到键值对（key,value）此时得到的键值对又叫做“中间结果”。此后便进入reduce阶段，由此可以看出Shuffle阶段的作用是处理“中间结果”。由于Shuffle涉及到了磁盘的读写和网络的传输，因此Shuffle性能的高低直接影响到了整个程序的运行效率。 MapReduce Shuffle Hadoop的核心思想是MapReduce，但shuffle又是MapReduce的核心。shuffle的主要工作是从Map结束到Reduce开始之间的过程。shuffle阶段又可以分为Map端的shuffle和Reduce端的shuffle。

spark学习

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总是学了就忘记，spark都学了几遍了总是深入不进去唉头疼这里再次学习一遍谁有更好的深入学习spark的方法给推荐推荐面试了大数据，盘点几个被问到的问题： spark一定会把中间结果放在内存吗？当然不是可以是内存，也可以是磁盘 spark包括work和master work和master之间的沟通通过网络RPC进行交流沟通拷贝到其他节点 for i in {5..7}; do scp -r /bigdata/spark/conf/spark-env.sh node-$i:$PWD; done spark是移动计算，而不移动数据因为大量数据移动成本大 spark是Scala 编写 spark包本身有Scala编译器和库但spark是运行在jvm上的需要安装jdk 利用zookeeper实现高可用集群 zookeeper用来1选举 2保存活跃的master信息 3 保存worker的资源信息和资源使用情况（为了故障切换转移）在env.sh中添加export SPARK_DAEMON_JAVA_OPTS="-Dspark .deploy.recoveryMode=ZOOKEEPER xxxzookeeper相关信息" 高可用的spark需要手动启动另一个(standby)spark-master 并不会随着spark-all.sh 启动master

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