[R] builtin to filter a list?

[Whit Armstrong]

?Filter ...

how did I miss that one?

Thanks, Gabor.

-Whit


On Wed, Oct 29, 2008 at 9:37 AM, Gabor Grothendieck
<ggrothendieck at gmail.com> wrote:
> 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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>> and provide commented, minimal, self-contained, reproducible code.
>>
>