private int unFilledSpacesInHeaderGroup(int header) {
        //If mNumColumns is equal to zero we will have a divide by 0 exception
        if(mNumColumns == 0){
            return 0;
        }

        int remainder = mDelegate.getCountForHeader(header) % mNumColumns;
        return remainder == 0 ? 0 : mNumColumns - remainder;
    }
Counts the number of items that would be need to fill out the last row in
the group of items with the given header.

@param header Header set of items are grouped by.
@return The count of unfilled spaces in the last row.
Library/src/com/tonicartos/widget/stickygridheaders/StickyGridHeadersBaseAdapterWrapper.java