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N-Gram Count

N-Gram Count exercise using Hadoop and Kotlin, explained in this blog post

The goal of this exercise is tuple count n-words at a time, with n coming from the terminal, filtering out n-grams that start with a user defined keyword, counting how many words have been removed.

What it is interesting of this exercise:

  • Use of NGramCombiner for reducing network operations.
  • Use of Properties and Counters for sharing data with Mapper, Reducer and Combiner.

In order tuple run this exercise on an Hadoop machine, the following commands are necessary:

hdfs dfsadmin -safemode leave

# Removes folders from the previous run
hdfs dfs -rm -r <input-folder>
hdfs dfs -rm -r <output-folder>

# Puts input data into hdfs
hdfs dfs -put <input-file>
# or for an entire folder
# hdfs dfs -put <input-folder>

hadoop jar 02_n-gram-count.jar Main <num_reducers> <input-file> <output-folder> <n> <keyword>
# or for an entire input folder
# hadoop jar 01_hello-big-data.jar Main <num_reducers> <input-folder> <output-folder> <n> <keyword>