docs: protected Vec[][] makeTemplates() {
      Vec anyVec = dataset.anyVec();
      final long[][] espcPerSplit = computeEspcPerSplit(anyVec._espc, anyVec.length());
      final int num = dataset.numCols(); // number of columns in input frame
      final int nsplits = espcPerSplit.length; // number of splits
      final String[][] domains = dataset.domains(); // domains
      final boolean[] uuids = dataset.uuids();
      final byte[] times = dataset.times();
      Vec[][] t = new Vec[nsplits][/*num*/]; // resulting vectors for all
      for (int i=0; i<nsplits; i++) {
        // vectors for j-th split
        t[i] = new Vec(Vec.newKey(),espcPerSplit[i/*-th split*/]).makeZeros(num, domains, uuids, times);
      }
      return t;
    }