[R] extract index during execution of sapply

[Martin Morgan]

Christian,

A favorite of mine is to use lexical scope and a 'factory' model:

> fun_factory <- function() {
+     i <- 0                  # 'state' variable(s), unique to each fun_factory
+     function(x) {           # fun_factory return value; used as sapply FUN
+         i <<- i + 1         # <<- assignment finds i
+         x^i                 # return value of sapply FUN
+     }
+ }
> 
> sapply(1:10, fun_factory())
 [1]           1           4          27         256        3125       46656
 [7]      823543    16777216   387420489 10000000000


Christian Bieli <christian.bieli at unibas.ch> writes:

> Hi there
> During execution of sapply I want to extract the number of times the 
> function given to supply has been executed. I came up with:
>
> mylist <- list(a=3,b=6,c=9)
> sapply(mylist,function(x)as.numeric(gsub("[^0-9]","",deparse(substitute(x)))))
>
> This works fine, but looks quite ugly. I'm sure that there's a more 
> elegant way to do this.
>
> Any suggestion?
>
> Christian
>
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-- 
Martin Morgan
Bioconductor / Computational Biology
http://bioconductor.org