CODEWITHSUNDEEP
rapply
tjnel
tjnel

Reputation: 683

Error using Apply Function in R on Tutorial Example

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"

Upvotes: 7

Views: 4773

Answers (1)

daikonradish
daikonradish

Reputation: 702

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.

Upvotes: 2

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