[R] Error with lapply [addirional clarification needed]

[Peter Dalgaard]

megh wrote:
> I need one more clarification here :
> 
> Here I did :
> 
> fn <- function(i) return(list(i, i^2))
> ss = sapply(1:4, fn)
> 
> Here the object "ss" should be a matrix object :
> is.matrix(ss)
> 
> However I feel it lacks some the matrix object properties. For example the
> syntax "min(ss[1,])" generates an error :
> "Error in min(ss[1, ]) : invalid 'type' (list) of argument".
> 
> What should be the way out? Am I missing something ?

ss is a dim'ed list object, because fn returns a list. This appears to 
be a feature, although rarely used. One point is that you can do

 > fn <- function(i) return(list(as.character(i), i^2))
 > ss <- sapply(1:4, fn)
 > ss
      [,1] [,2] [,3] [,4]
[1,] "1"  "2"  "3"  "4"
[2,] 1    4    9    16
 > ss[,1]
[[1]]
[1] "1"

[[2]]
[1] 1

I.e., the rows can be of different mode.

The easiest way out is just not to do that, i.e. return a vectore c(i, 
i^2) instead.


-- 
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