def findAllBycolumn(self, target):
        """ Returns an array of columns in the region (defined by the raster), each
        column containing all matches in that column for the target pattern. """
        column_matches = []
        for column_index in range(self._raster[1]):
            column = self.getRow(column_index)
            column_matches[column_index] = column.findAll(target)
        return column_matches
Returns an array of columns in the region (defined by the raster), each
        column containing all matches in that column for the target pattern.