Grid Based Puzzle Board Game Block Removal Algorithm?

the rules are that same coloured blocks of two or more can be removed by clicking on them. blocks then slide down from above. if a column is empty columns other columns move in from the sides.when someone clicks on the green blocks in the bottom row the columns should slide in from the sides. columns to the left of the black line slide right and on the right of the black line slide left. so in this case only the two rightmost columns should slide from the right to the black line after removing the green blocks.The problem i am having is in designing a suitable algorihm to do the collapsing after the removal. my current approach is to test each column from left to right to see if it is empty. if it is empty then i slide whatever column is to the left (if left of the black line) or to the right (if to the right of the black line) over the blank column and repeat this in the direct i am sliding from