code: public static <T> DataSet<T> sampleWithSize(
  		DataSet <T> input,
  		final boolean withReplacement,
  		final int numSamples) {
  
  		return sampleWithSize(input, withReplacement, numSamples, Utils.RNG.nextLong());
  	}
docs: Generate a sample of DataSet which contains fixed size elements.
  
  <p><strong>NOTE:</strong> Sample with fixed size is not as efficient as sample with fraction, use sample with
  fraction unless you need exact precision.
  
  @param withReplacement Whether element can be selected more than once.
  @param numSamples       The expected sample size.
  @return The sampled DataSet