docs: static public DHistogram[] initialHist(Frame fr, int ncols, int nbins, DHistogram hs[], int min_rows, boolean doGrpSplit, boolean isBinom) {
      Vec vecs[] = fr.vecs();
      for( int c=0; c<ncols; c++ ) {
        Vec v = vecs[c];
        final float minIn = (float)Math.max(v.min(),-Float.MAX_VALUE); // inclusive vector min
        final float maxIn = (float)Math.min(v.max(), Float.MAX_VALUE); // inclusive vector max
        final float maxEx = find_maxEx(maxIn,v.isInt()?1:0); // smallest exclusive max
        final long vlen = v.length();
        hs[c] = v.naCnt()==vlen || v.min()==v.max() ? null :
          make(fr._names[c],nbins,(byte)(v.isEnum() ? 2 : (v.isInt()?1:0)),minIn,maxEx,vlen,min_rows,doGrpSplit,isBinom);
      }
      return hs;
    }