How to save a chart object created in loops

Question

I have a chart created inside a couple of loops and I want to automatically write the chart to a file at the end of the outer loop. Here is a toy example:

filename <- "mychart"
for(i in 1:5) {
  x <- 1:5
  fun1 <- sample(1:10, 5, replace = TRUE)
  xlim <- c(1, 5)
  ylim <- c(0, 10)
  plot(x, fun1, xlim = xlim, ylim = ylim, type = "l")
  for(j in 1:3)  {
    fun2 <- 2:6 + j
    lines(x, fun2, type = "l", col = "red")
  }
  out.filename <- paste(filename, i, sep = "")
  ## want to save this plot out to disk here!
}

I would also like to create the plot on the console so I can watch the program’s progress. Most answers to a similar question seem to deal with a plot that is created with a single “plot” statement, or do not enable the console plot window. Any suggestions much appreciated.

Answer 1

I think this does what you're after:

plotit <- function(i) {
   x = 1:5
   fun1 = sample(1:10, 5, replace=TRUE)
   plot(x, fun1, xlim=c(1,5), ylim=c(0,10), type="l")
   for(j in 1:3)  {
       fun2 = 2:6 + j
       lines(x, fun2, type = "l", col = "red")
   }   
   savePlot(paste0("mychart", i, ".png"), type="png")
}

Then:

for(i in seq(5)) plotit(i)

Answer 2

The typical way to save base graphics plots is with individual device functions such as pdf(), png(), etc. You open a plot device with the appropriate filename, create your plot, then close the device with dev.off(). It doesn't matter if your plot is created in a for loop or not. See lots of devices (and examples at the bottom) in ?png.

For your code, it would go something like this:

filename <- "mychart"
for(i in 1:5) {

    out.filename <- paste(filename, i, ".png", sep = "")
    ## Open the device before you start plotting
    png(file = out.filename)
    # you can set the height and width (and other parameters) or use defaults

    x <- 1:5
    fun1 <- sample(1:10, 5, replace = TRUE)
    xlim <- c(1, 5)
    ylim <- c(0, 10)
    plot(x, fun1, xlim = xlim, ylim = ylim, type = "l")
    for(j in 1:3)  {
        fun2 <- 2:6 + j
        lines(x, fun2, type = "l", col = "red")
    }
    ## Close the device when you are done plotting.
    dev.off() 
}