Are you sure things are set up the way you intend? Here are some things I've noticed:
1) Your main problem is that you're defining idx with a column (size from 1155 to 7159), but your final call is looking at a row, so you're switching your indices. You only have 10 columns, but idx is sized from 1155 to 7159.
2) Although ismember works, you're going to get a return of a logic array for all elements in the specific column. It might be a bit more concise to call find() to just get the desired indices. This might be a personal preference thing for my coding style.
3) idx looks at specific elements of your top level cell array, but your final call looks only at the first cell. This will cause you problems when you have idx coming from a cell with more columns than s(1,1).