code: public static void extractChunkPart(Chunk ic, Chunk oc, int startRow, int nrows, Futures fs) {
      try {
        NewChunk dst = new NewChunk(oc);
        dst._len = dst._sparseLen = 0;
        // Iterate over values skip all 0
        ic.extractRows(dst, startRow,startRow+nrows);
        // Handle case when last added value is followed by zeros till startRow+nrows
        assert dst._len == oc._len : "NewChunk.dst.len = " + dst._len + ", oc._len = " + oc._len;
        dst.close(dst.cidx(), fs);
      } catch(RuntimeException t){
        Log.err("got exception in chunkSplitter, ic = " + ic + ", oc = " + oc + " startRow = " + startRow + " nrows = " + nrows);
        throw t;
      }
    }
docs: Extract portion of given chunk into given output chunk.