product listing: change number of columns based on category?

Hello everyone,

I tried to find a topic about it but I can't...
Do you know how to change dynamically the number of products in a row (in the product listing)?

I explain what I want: in the product listing I would like a number of products in a row which can different depends on the category.

For exemple: for the category "bags" I would like 3 products per row and for the category "earrings" I would like 5 products per row.

Do you know how I can do that??

Thanks a lot,

Francois