Error using Apply Function in R on Tutorial Example - r

Question

I am trying to learn about how to use the apply function and I came across this tutorial: http://nsaunders.wordpress.com/2010/08/20/a-brief-introduction-to-apply-in-r/ which seems clear and concise, but I'm running into a problem right away. The very first example they give to demonstrate apply is:
> # create a matrix of 10 rows x 2 columns
> m <- matrix(c(1:10, 11:20), nrow = 10, ncol = 2)
> # mean of the rows
> apply(m, 1, mean)
[1] 6 7 8 9 10 11 12 13 14 15
This seems very basic, but I thought I'd give it a try. Here is my result:
> # create a matrix of 10 rows x 2 columns
> m <- matrix(c(1:10, 11:20), nrow = 10, ncol = 2)
> # mean of the rows
> apply(m, 1, mean)
Error in FUN(newX[, i], ...) : unused argument(s) (newX[, i])
Needless to say, I'm lost on this one...
To provide some more information, I attempted another example provided in the tutorial and got the correct result. The difference in this case was that the function was specifically stated in the apply function:
apply(m, 1:2, function(x) x/2)
[,1] [,2]
[1,] 0.5 5.5
[2,] 1.0 6.0
[3,] 1.5 6.5
[4,] 2.0 7.0
[5,] 2.5 7.5
[6,] 3.0 8.0
[7,] 3.5 8.5
[8,] 4.0 9.0
[9,] 4.5 9.5
[10,] 5.0 10.0
sessionInfo() output is below:
R version 2.15.3 (2013-03-01)
Platform: x86_64-apple-darwin9.8.0/x86_64 (64-bit)
locale:
[1] en_US.UTF-8/en_US.UTF-8/en_US.UTF-8/C/en_US.UTF-8/en_US.UTF-8
attached base packages:
[1] stats graphics grDevices utils datasets methods base
loaded via a namespace (and not attached):
[1] tools_2.15.3
And the output for conflicts(details = TRUE)
$.GlobalEnv
[1] "edit" "mean"
$`package:utils`
[1] "edit"
$`package:methods`
[1] "body<-" "kronecker"
$`package:base`
[1] "body<-" "kronecker" "mean"

Answer 1

As others have identified, it's probably because you have a conflict on mean. When you call anything (functions, objects), R goes through the search path until it's found (and if it isn't found R will complain accordingly):
> search()
[1] ".GlobalEnv" "tools:RGUI" "package:stats"
[4] "package:graphics" "package:grDevices" "package:utils"
[7] "package:datasets" "package:methods" "Autoloads"
[10] "package:base"
If you're fairly new to R, note that when you create a function, unless you specify otherwise, it's usually going to live in ".GlobalEnv". R looks there first before going any further, so it's fairly important to name your functions wisely, so as not to conflict with common functions (e.g. mean, plot, summary).
It's probably a good idea to start with a clean session once in a while. It's fairly common in the debugging phase to name variables x or y (names picked for convenience rather than informativeness... we're only human after all), which can be unexpectedly problematic down the line. When you have a workspace that's fairly crowded, the probability of conflicts increases, so (a) pick names carefully and (b) restart without restoring would be my advice.