I agree with the cyclist in that you probably don't really need to do this in your next step, whatever it is.
That said, you can use sparse() but I really, really doubt you want to, or need to, do that.
If you just want to print it out to the command line, you can use a loop with fprintf() and just print those that are 1 and print a space for the zeros.
But a matrix cannot have "holes" or "ragged edges". There has to be something there.