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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"
445
Apply functions are a family of functions in base R which allow you to repetitively perform an action on multiple chunks of data. An apply function is essentially a loop, but run faster than loops and often require less code.
apply() function apply() takes Data frame or matrix as an input and gives output in vector, list or array. Apply function in R is primarily used to avoid explicit uses of loop constructs. It is the most basic of all collections can be used over a matrice. The simplest example is to sum a matrice over all the columns.
In R Programming Language to apply a function to every integer type value in a data frame, we can use lapply function from dplyr package. And if the datatype of values is string then we can use paste() with lapply.
You can use the help section to get a description of this function. the apply function looks like this: apply(X, MARGIN, FUN).
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.
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