subset of rows used to plot. It can be an index vector, or the length of a random subset
main
title of the plot
Details
To increase the plot efficiency, by default, we only plot RANDOMLY selected subset of points (based on parameter "subset"). If users want to plot all the points, they can set the parameter "subset = NULL". When smoothScatter is set as TRUE, the subsetting will be suppressed because smoothScatter function has good plot efficiency for large number of points.