A trap for young players with the lapply() function.
On Mon, 27 Mar 2017, Rolf Turner wrote:
From time to time I get myself into a state of bewilderment when using
apply() by calling it with FUN equal to a function which has an "optional"
argument named "X".
E.g.
xxx <- lapply(y,function(x,X){cos(x*X)},X=2*pi)
which produces the error message
Error in get(as.character(FUN), mode = "function", envir = envir) : object 'y' of mode 'function' was not found
This of course happens because the name of the first argument of lapply() is "X" and so it takes the value of this first argument to be the supplied X (2*pi in the foregoing example) and then expects what the user has denoted by "y" to be the value of FUN, and (obviously!) it isn't.
The lapply help page addresses this issue in `Details' :
"it is good practice to name the first two arguments X and FUN if ... is
passed through: this both avoids partial matching to FUN and ensures that
a sensible error message is given if arguments named X or FUN are passed
through ..."
So that advice suggests something like:
xxx <- lapply( X=y, FUN=function(X,x){cos(X*x)}, x=2*pi )
Best,
Chuck