Let's say I'm trying to have the user input a data frame into R Shiny as a .RData object. I don't know how many columns it contains. I want to create a histogram for each column. If I knew the number of columns, I could just create a PlotOutput for each histogram I needed in the UI <- fluidPage() part of the code. I think the best option may be to somehow combine all the histograms into one plot object--how would I go about doing that?