code: public INDArray outputSingle(DataSetIterator iterator){
          Preconditions.checkArgument(numOutputArrays == 1, "Cannot use this method with nets that have more" +
                  " than 1 output array. This network has %s outputs", numOutputArrays);
          return output(iterator)[0];
      }
docs: Generate the output for all examples/batches in the input iterator, and concatenate them into a single array.
  Can only be used with ComputationGraphs with 1 output
  
  @param iterator Data to pass through the network
  @return output for all examples in the iterator