On Tue, Oct 8, 2013 at 10:22 AM, Asis Hallab <asis.hal...@gmail.com> wrote:
> Dear R-Experts,
> So, what is the difference between Reduce and do.call and when best to
> use which?
>From the help:
‘Reduce’ uses a binary function to successively combine the
elements of a given vector and a possibly given initial value.
‘do.call’ constructs and executes a function call from a name or a
function and a list of arguments to be passed to it.
In your example, rbind gets called N-1 times when using Reduce (where
N is the length of the list) because it is doing something like:
rbind(x[[1]],rbind(x[[2]],x[[3]]))
For longer lists, its doing something like (where a b c d e are list
elements x[[1]] to x[[5]])
rbind( a, rbind( b, rbind( c, rbind( d, e ) ) ) )
whereas do.call calls it once, as rbind(a,b,c,d,e)
Use Reduce when you are doing a Reduce operation (read up on
Functional Programming). Use do.call when you want to call a function
with parameters in a list.
Barry
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