Thank you for your effort.   No, this file is not empty: here you can check it part-r-00000   I would like to see all the vectors with information about cluster for each.   It would be nice to see also centers of the clusters.   I changed     IntWritable key = new IntWritable(); WeightedPropertyVectorWritable value = new WeightedPropertyVectorWritable();  to this   Text key = new Text(); ClusterWritable value = new ClusterWritable();  I have not got any exception but the oputput is:   org.apache.mahout.clustering.iterator.ClusterWritable@572c4a12 belongs to cluster C-0 org.apache.mahout.clustering.iterator.ClusterWritable@572c4a12 belongs to cluster C-1  --- EDIT:   I changed   value.toString()  to   value.getValue()  and now, I have got an output:   C-0: {0:0.07,1:0.9499999999999998} belongs to cluster C-0 C-1: {0:12.25,1:12.9} belongs to cluster C-1   Thank you very much !!!! ... View more