[R] execute array of functions

[David Winsemius]

On Feb 14, 2012, at 2:32 PM, Stavros Macrakis wrote:

> That won't work because R has special rules for evaluating things in  
> the
> function position.  Examples:
>
> *OK*
>
> min(1:2)
> "min"(1:2)
> f<-min; f(1:2)
> do.call(min,list(1:2))
> do.call("min",list(1:2))      # do.call converts string->function
>
>
> *Not OK*
>
> ("min")(1:2)              # string in function position is not  
> converted
> f<-"min"; f(1:2)       # ditto
> f<- c("min","max");  f[1](1:2)  # ditto
>
>
> What you need to do is make 'f' a list of *function values, *not a  
> vector
> of strings:
>
> f<- c(min,max)
>
>
> and then select the element of f with [[ ]] (select one element),  
> not [ ]
> (select sublist):
>
> f[[1]](1:2)
>
>
> Thus your example becomes
>
> type    <- c(min,max)
> n       <- 1:10
> for (a in 1:2)    {
> print(type[[a]](n)) }
>
> Another (uglier) approach is with do.call:
>
> type    <- c("min","max")
> n       <- 1:10
> for (a in 1:2)    {
> print(do.call(type[a],list(n))) }

This is somewhat less ugly:

  funs <- c("min","max")
  for (a in funs) 	  {
    print(do.call(a, list(n))) }

[1] 1
[1] 10

>
>
> Does that help?
>
>             -s
>
> On Tue, Feb 14, 2012 at 14:02, Muhammad Rahiz
> <muhammad.rahiz at ouce.ox.ac.uk>wrote:
>
>> Hi all,
>>
>> I'm trying to get the min and max of a sequence of number using a  
>> loop
>> like the folllowing. Can anyone point me to why it doesn't work.
>>
>> Thanks.
>>
>> type    <- c("min","max")
>> n       <- 1:10
>> for (a in 1:2)    {
>> print(type[a](n)) }
>>
>>
>> --
>> Muhammad
>>
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>>
>
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>
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David Winsemius, MD
West Hartford, CT