presto-main/src/main/java/io/prestosql/operator/WindowOperator.java/WindowOperator/rearrangePage
class WindowOperator:    private static Page rearrangePage(Page page, int[] channels)
    {
        Block[] newBlocks = new Block[channels.length];
        for (int i = 0; i < channels.length; i++) {
            newBlocks[i] = page.getBlock(channels[i]);
        }
        return new Page(page.getPositionCount(), newBlocks);
    }