Re: [R] Counterpart for Matlab's 'feval'?

From: Barry Rowlingson <B.Rowlingson_at_lancaster.ac.uk>
Date: Fri 24 Jun 2005 - 19:44:09 EST

Robin Hankin wrote:

>>I've just begun writing a program that searches for the minimum of a
>>function with golden section search. In order to do this in a nice way  
>>I
>>need a function that takes a function name and an argument and returns  
>>the
>>function value for that argument, i .e just like Matlab's 'feval'. Is
>>there any?

It might be better to write a function that takes a function as an argument, instead of the function name:

> doit = function(f,...){f(...)}
> doit(sqrt,2)

  [1] 1.414214
> doit(sum,1,2,3)

  [1] 6

This way you can write little inline anonymous functions:

> doit(function(a,b,c){a^3+b^2+c},1,4,3)
  [1] 20

The equivalent way with do.call, and function names is:

> docall=function(fc,...){do.call(fc,list(...))}
> docall("sqrt",2)

  [1] 1.414214
> docall("sum",1,2,3)

  [1] 6

But:

> docall("function(a,b,c){a^3+b^2+c}",1,4,3)
  Error in do.call(fc, list(...)) : couldn't find function "function(a,b,c){a^3+b^2+c}"

This can be fixed by using eval and parse instead:

> doe=function(fc,...){eval(parse(text=fc))(...)}
> doe("sqrt",2)

  [1] 1.414214
> doe("sum",1,2,3)

  [1] 6
> doe("function(a,b,c){a^3+b^2+c}",1,4,3)
  [1] 20

I see other solutions have been posted already. They're probably better.

Baz



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https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html Received on Fri Jun 24 19:47:10 2005

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