simplest_mapreduce_bash_wordcount.ipynb

{
 "cells": [
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# Simple distributed wordcount with MapReduce"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Check that file `file.txt` exists, view size."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "!ls -hal file.txt"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Copy file to HDFS"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "!hdfs dfs -put -f file.txt "
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Erase `result` folder."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "!hdfs dfs -rm -R result 2>/dev/null"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Run the bash wordcount command `wc` in parallel on the distributed file."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "!mapred streaming \\\n",
    "  -input file.txt \\\n",
    "  -output result \\\n",
    "  -mapper /bin/cat \\\n",
    "  -reducer /usr/bin/wc "
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Check result of MapReduce job"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "!hdfs dfs -cat result/part*"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Check that the word count is correct by comparing with `wc` on local host (warning: do not try with too large files)."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "!wc file.txt"
   ]
  }
 ],
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