R help - Oct 2008 - builtin to filter a list?

I know it's easy to write a simple loop to do this, but in the spirit
of lapply, I thought I would ask if there is a builtin to filter or
take a subset of a list based on a predicate in a similar way to the
Erlang lists:filter/2 function:

http://www.erlang.org/doc/man/lists.html#filter-2

filter(Pred, List1) -> List2
Types:

Pred = fun(Elem) -> bool()
 Elem = term()
List1 = List2 = [term()]
List2 is a list of all elements Elem in List1 for which Pred(Elem) returns true.

I've tried the simple case in R already:
> x <- rnorm(10)
> xl <- as.list(x)
> xl[[ x > 0]]
Error in xl[[x > 0]] : attempt to select less than one
element
>
Thanks,
Whit

Try:

?Filter

e.g.

Filter(function(x) x > 0, x1)

or  using gsubfn's fn

library(gsubfn)
fn$Filter(~ x > 0, x1)


On Wed, Oct 29, 2008 at 9:06 AM, Whit Armstrong
<armstrong.whit at gmail.com> wrote:
> I know it's easy to write a simple loop to do this, but in the spirit
> of lapply, I thought I would ask if there is a builtin to filter or
> take a subset of a list based on a predicate in a similar way to the
> Erlang lists:filter/2 function:
>
> http://www.erlang.org/doc/man/lists.html#filter-2
>
> filter(Pred, List1) -> List2
> Types:
>
> Pred = fun(Elem) -> bool()
>  Elem = term()
> List1 = List2 = [term()]
> List2 is a list of all elements Elem in List1 for which Pred(Elem) returns
true.
>
> I've tried the simple case in R already:
>
>> x <- rnorm(10)
>> xl <- as.list(x)
>> xl[[ x > 0]]
> Error in xl[[x > 0]] : attempt to select less than one element
>>
>
> Thanks,
> Whit
>
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