R random binary dataframe with fixed column sums

So I'm trying to build a dataframe, that is entirely composed of 1s and 0s. It should be randomly built except for the fact that each column needs to add up to a specified value.

I would know how to do this if this was for just one dataframe, but it needs to be built into a function, where in said function it will be done as an iterative process, up to 1000x.