Print j on every outside loop iteration in R

Question

For the following code: I can't figure out why j does not print on every outside loop iteration.

x = 0

for (j in 1:15)
{
for (i in 1:100000)
{
x = x + 1
}
print(j)
}

What R seems to be doing is running the the whole thing, and at the end print out all the js, not one by one as when every loop iterates.

It seems to be that j should be printing after every loop iteration, what am I missing here?

Is there a way to make it such that j in printed on every outside loop iteration?

Thank You

Answer 1

I'm guessing you are using the Windows Rgui, which buffers its console output, and then writes it out in chunks (see the R Windows FAQ 7.1). To force immediate printing to the console, you can simply add a call to flush.console() after the print() statement.

x = 0

for (j in 1:15) {
    for (i in 1:100000) {
        x = x + 1
    }
    print(j)
    flush.console()
}

Answer 2

R output is typically buffered. You can circumvent this in two ways. Either (only on Windows, IIRC) you can go to the menu of the R Gui, and chose Misc -> Buffered Output (or press Ctrl-W) to disable buffering (which typically slows down execution), or you can call flush.console() any time you want to ensure that the output is actually shown (e.g. to show progress).

Answer 3

Not familiar with R but that code looks right for what you are trying to do. May be something to do with output buffering as I've come accross the same issue in PHP where the whole script runs before any output is rendered.