save multiple plots in R as a .jpg file, how?

Question

I am very new to R and I am using it for my probability class. I searched for this question here, but it looks that is not the same as I want to do. (If there is already an answer, please tell me).

The problem is that I want to save multiple plots of histograms in the same file. For example, if I do this in the R prompt, I get what I want:

library(PASWR)
data(Grades)
attach(Grades) # Grade has gpa and sat variables
par(mfrow=c(2,1))
hist(gpa)
hist(sat)

So I get both histograms in the same plot. but if I want to save it as a jpeg:

library(PASWR)
data(Grades)
attach(Grades) # Grades has gpa and sat variables

par(mfrow=c(2,1))
jpeg("hist_gpa_sat.jpg")
hist(gpa)
hist(sat)
dev.off()

It saves the file but just with one plot... Why? How I can fix this? Thanks.

Also, if there is some good article or tutorial about how to plot with gplot and related stuff it will be appreciated, thanks.

Answer 1

Swap the order of these two lines:

par(mfrow=c(2,1))
jpeg("hist_gpa_sat.jpg")

so that you have:

jpeg("hist_gpa_sat.jpg")
  par(mfrow=c(2,1))
  hist(gpa)
  hist(sat)
dev.off()

That way you are opening the jpeg device before doing anything related to plotting.