• Big Data


  • hadoop
  • java

Matrices Sum Map Reducer
Matrix sum is the operation of adding matrices by adding corresponding entries together.
Entrywise sum
The sum of two m × n (pronounced “m by n”) matrices A and B, denoted by A + B, is again an m × n matrix computed by adding corresponding elements
matraix sum

Entrywise sum implementation using Map-reduce-

I have two matrices in separate files ( check blog indexingfor generating index), each file contains same size (m*n) matrix. matrix row index(m) and values separated by ^A [0x001] and values(n) are separated by (,).

  1. Mapper emits the row index as key and entire row as a value. If you have different types of matrices then create separate mappers to process/ filters the matrix.
    class MatrixSumMapper extends Mapper\<LongWritable, Text, LongWritable, Text\> { String fName = null; char keySeprator; @Override protected void setup( Mapper\<LongWritable, Text, LongWritable, Text\>.Context context) throws IOException, InterruptedException { fName = ((FileSplit)context.getInputSplit()).getPath().getName(); keySeprator=(char)context.getConfiguration().getInt("matrix.key.separator",0x001); } @Override protected void map(LongWritable key, Text value, Mapper\<LongWritable, Text, LongWritable, Text\>.Context context) throws IOException, InterruptedException { LongWritable keyM = new LongWritable(Long.parseLong(value.toString().split(String.format("%c",keySeprator))[0])); Text val = new Text(value.toString().split(String.format("%c",keySeprator))[1]); context.write(keyM, val); } }
  2. Reducer gets the row key as (m). Next split each value to generate (n) then add the values index and position wise.
    class MatrixSumReducer extends Reducer\<LongWritable, Text, LongWritable, Text\> { String vseparator; String fseparator; private static Logger logger = Logger.getLogger(MatrixSumMapper.class); @Override protected void setup( Reducer\<LongWritable, Text, LongWritable, Text\>.Context context) throws IOException, InterruptedException { logger.debug("reducer- setup: begin"); vseparator = context.getConfiguration().get("matrix.element.separator"); logger.debug("reducer- setup: end"); } @Override protected void reduce(LongWritable key, Iterable value, Reducer\<LongWritable, Text, LongWritable, Text\>.Context ctxt) throws IOException, InterruptedException { List\<Integer[]\> matrixValues = new ArrayList\<Integer[]\>(); List val = new ArrayList(); for (Text t : value) { prepareKeyValueMap(t, matrixValues); } for (Integer[] i : matrixValues) { for (int j = 0; j \< i.length; j++) { try{ int sum = val.remove(j); val.add(j,sum+i[j]); }catch(Exception e){ System.out.println("throwing exception"); val.add(i[j]); } } } ctxt.write(key, new Text(val.toString())); } private void prepareKeyValueMap(Text value, List\<Integer[]\> valuesLst) { String[] valuesStr = value.toString().split(vseparator); Integer[] valuesInt = new Integer[valuesStr.length]; for (int i = 0; i \< valuesStr.length; i++) { try { valuesInt[i] = Integer.parseInt(valuesStr[i]); } catch (NumberFormatException e) { logger.error(e.getMessage()); } } valuesLst.add(valuesInt); } }
  3. Driver code:
    public class Driver extends Configured implements Tool { private static Logger logger = Logger.getLogger(Driver.class); private boolean deleteDirectory(Path path) throws IOException { FileSystem fs = FileSystem.get(getConf()); return fs.delete(path, true); } public int run(String[] args) throws Exception {"job Matrix Sum Driver Begin"); Configuration conf = getConf(); conf.setInt("matrix.key.separator", 0x001); conf.set("matrix.element.separator",","); Job job = new Job(conf, "Matrix Sum"); job.setJarByClass(Driver.class); Path input1 = new Path(args[0]); Path input2 = new Path(args[1]); Path output = new Path(args[2]); deleteDirectory(output); job.setMapOutputKeyClass(LongWritable.class); job.setMapOutputValueClass(Text.class); job.setMapperClass(MatrixSumMapper.class); job.setReducerClass(MatrixSumReducer.class); job.setNumReduceTasks(1); job.setInputFormatClass(TextInputFormat.class); job.setOutputFormatClass(TextOutputFormat.class);"deleting output directory: " + deleteDirectory(output)); FileInputFormat.setInputPaths(job, input1, input2); FileOutputFormat.setOutputPath(job, output); return job.waitForCompletion(true) ? 0 : 1; } public static void main(String[] args) throws Exception { for (String str : args) System.out.println(str); Configuration config = new Configuration(); System.exit(, new Driver(), args)); } }

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