Rhadoop - wordcount using rmr

Question

I am trying to run a simple rmr job using Rhadoop package but it is not working.Here is my R script

print(\"Initializing variable.....\")
Sys.setenv(HADOOP_H         


        

Answer 1

Firstly, you'll have to set the HADOOP_STREAMING environment variable in your code.

Try the below code, and note that the code assumes that you have copied your text file to the hdfs folder examples/wordcount/data

R Code:

Sys.setenv("HADOOP_CMD"="/usr/local/hadoop/bin/hadoop")
Sys.setenv("HADOOP_STREAMING"="/usr/local/hadoop/share/hadoop/tools/lib/hadoop-streaming-2.4.0.jar")

# load librarys
library(rmr2)
library(rhdfs)

# initiate rhdfs package
hdfs.init()

map <- function(k,lines) {
  words.list <- strsplit(lines, '\\s')
  words <- unlist(words.list)
  return( keyval(words, 1) )
}

reduce <- function(word, counts) {
  keyval(word, sum(counts))
}

wordcount <- function (input, output=NULL) {
  mapreduce(input=input, output=output, input.format="text", map=map, reduce=reduce)
}

## read text files from folder example/wordcount/data
hdfs.root <- 'example/wordcount'
hdfs.data <- file.path(hdfs.root, 'data')

## save result in folder example/wordcount/out
hdfs.out <- file.path(hdfs.root, 'out')

## Submit job
out <- wordcount(hdfs.data, hdfs.out) 

## Fetch results from HDFS
results <- from.dfs(out)
results.df <- as.data.frame(results, stringsAsFactors=F)
colnames(results.df) <- c('word', 'count')

head(results.df)

Output:

word count
  AS    16
  As     5
  B.     1
  BE    13
  BY    23
  By     7

For your reference, here is another example of running R word count map reduce program.

Hope this helps.