Question

Possible Duplicate:
How to be alerted about the ongoing progress of a loop/lapply

While debugging a R program, I would like to print the output information to the screen for the debugging purposes. For instance, how to generate something like the following in the same line.

"loop= 5", "a=5","b=5"

Answer 1

Taking @Matthew’s suggestion, the problem may just be that you are attempting to use print on several variables/strings at once. This wont work.

If you want to use print with strings, you need to give one, single string. And the most effective way of doing this is using paste().
There are also many alternatives, such as cat and sprintf. Here is a brief example:

Let’s create some sample variables to output
i <- 3
a <- letters[1:5]

You may be trying to do this:

# This will *NOT* work
print("loop = ", i, "a = ", a[[i]])

Instead try one of the following:
(note: paste0 is the same as using paste(..., sep=""))

# using print( paste0 (.) )
print(paste0("loop = ", i, ", a = ", a[[i]]))
#  [1] "loop = 3, a = c

# using cat()
cat("loop = ", i, ", a = ", a[[i]])
#  loop =  3 , a =  c

# using sprintf
sprintf("loop = %d, a = %s", i, a[[i]])
#  [1] "loop = 3, a = c"