thanks Steve Loughran and Amr Shahin Amr Shahin , i refered " http://my.safaribooksonline.com/book/databases/hadoop/9780596521974/serialization/id3548156"; the same thing only. but my toString is not returning anything.
On Thu, Oct 31, 2013 at 5:57 PM, Amr Shahin <[email protected]> wrote: > Check this out: > http://developer.yahoo.com/hadoop/tutorial/module5.html#writable-notes > It shows how to create a customer writable. If you have "hadoop the > definitive guide" there is a really good explanation about custom data > types. > > Happy Halloween > > > On Thu, Oct 31, 2013 at 3:03 PM, unmesha sreeveni <[email protected] > >wrote: > > > this is my post from stackoverflow > > but i am not getting any response. > > > > > > I need to emit a 2D double array as key and value from mapper.There are > > questions posted in stackoverflow. But they are not answered. > > we have to create a custom datatype.but how?I am new to these custom > > datatypes. i dnt have any idea where to start.I am doing some of the > matrix > > multiplication in a given dataset.and after that i need to emit the value > > of > > A*Atrns which will be a matrix and Atrans*D which will also be a > matrix.so > > how to emit these matrices from mapper.And the value should be > > corresponding to the key itself.I think for that we need to use > > WritableComparable. > > > > > > > > public class MatrixWritable implements > WritableComparable<MatrixWritable>{ > > > > /** > > * @param args > > */ > > private double[][] value; > > > > public MatrixWritable() { > > // TODO Auto-generated constructor stub > > set(new double[0][0]); > > } > > > > public MatrixWritable(double[][] value) { > > // TODO Auto-generated constructor stub > > this.value = value; > > } > > > > public void set(double[][] value) { > > this.value = value; > > } > > > > public double[][] getValue() { > > return value; > > } > > > > @Override > > public void write(DataOutput out) throws IOException { > > System.out.println("write"); > > int row=0; > > int col=0; > > for(int i=0; i<value.length;i++){ > > row = value.length; > > for(int j=0; j<value[i].length; j++){ > > col = value[i].length; > > } > > } > > out.writeInt(row); > > out.writeInt(col); > > > > System.out.println("\nTotal no of observations: "+row+":"+col); > > > > for(int i=0;i<row ; i++){ > > for(int j= 0 ; j< col;j++){ > > > > out.writeDouble(value[i][j]); > > } > > } > > //priting array > > for(int vali =0;vali< value.length ;vali ++){ > > for(int valj = 0;valj <value[0].length;valj++){ > > System.out.print(value[vali][valj]+ "\t"); > > } > > System.out.println(""); > > } > > > > } > > > > @Override > > public void readFields(DataInput in) throws IOException { > > int row = in.readInt(); > > int col = in.readInt(); > > > > double[][] value = new double[row][col]; > > for(int i=0;i<row ; i++){ > > for(int j= 0 ; j< col;j++){ > > value[i][j] = in.readDouble(); > > > > } > > } > > > > } > > > > @Override > > public int hashCode() { > > > > } > > > > @Override > > public boolean equals(Object o) { > > > > } > > > > > > @Override > > public int compareTo(MatrixWritable o) { > > // TODO Auto-generated method stub > > return 0; > > } > > @Override > > public String toString() { > > > > return Arrays.toString(value); > > > > } > > > > > > > > } > > > > I wrote matrix write,readfields and toString. > > > > 1.But my toString is not returning anything. why is it so? > > > > 2.How to print these values with in Reducer ?I tried doing(tried with > > emiting only custom value- for checking) > > > > public class MyReducer extends > > > > > > Reducer<MatrixWritable, MatrixWritable, IntWritable, Text> { > > > > public void reduce(Iterable<MatrixWritable> key, > > Iterable<MatrixWritable> values, Context context){ > > for(MatrixWritable c : values){ > > > > System.out.println("print value "+c.toString()); > > > > } > > > > } > > > > but Nothing is printing.when i tried to print value[0].length in > toString() > > method it showsArrayIndexOutOfBoundExcep.Am i doing any thing wrong.and i > > also needed to print my data asmatrix so i tried > > > > public String toString() { > > > > String separator = ", "; > > StringBuffer result = new StringBuffer(); > > > > // iterate over the first dimension > > for (int i = 0; i < value.length; i++) { > > // iterate over the second dimension > > for(int j = 0; j < value[i].length; j++){ > > result.append(value[i][j]); > > System.out.print(value[i][j]); > > result.append(separator); > > } > > // remove the last separator > > result.setLength(result.length() - separator.length()); > > // add a line break. > > result.append("\n"); > > } > > > > > > return result.toString(); > > > > > > } > > > > Again my output is empty. 3.Inorder to emit a key too as custom datatype > > CompareTo is neccessary right . > > > > 4.so what should i include in that methods CompareTo,hashcode,equals and > > what are these methods intended for. > > Any Idea.Pls suggest a solution. > > > > -- > > *Thanks & Regards* > > * > > * > > Unmesha Sreeveni U.B* > > * > > *Junior Developer > > * > > *Amrita Center For Cyber Security > > * > > * > > Amritapuri. > > > > www.amrita.edu/cyber/ > > * > > > -- *Thanks & Regards* * * Unmesha Sreeveni U.B* * *Junior Developer * *Amrita Center For Cyber Security * * Amritapuri. www.amrita.edu/cyber/ *
