Loop Through Table IDs?

I have a PHP script that generates a large, tree structured, table from XML data.Depending on user input, I need to expand or collapse sections of the table (Show/Hide).The way I have written the PHP script, each row is labelled with an "id=" according to its tree position.e.g. block0, block0_0, block0_1, block1, block1_2_0, etc. The buttons for each branch of the tree call a Javascript function, e.g. onclick="return toggleMe('block1')" or onclick="return toggleMe('block2_0_1')", and the toggleMe function knows it has to Show/Hide every row who's id starts with that string. Each row has a unique id, just incrementing the last digit.My problem is that I do not know how many rows there are and what I want to do is to loop through all the rows and see if their id starts with the parameter sent to the function.