docs: public INDArray array() {
          List<INDArray> retList = new ArrayList<>(list.size());
          for(X x : list) {
              INDArray arr = x.array();
              retList.add(arr.reshape(1, arr.length()));
          }
  
          return Nd4j.concat(0,retList.toArray(new INDArray[retList.size()]));
      }