[R] extracting elements from a list in vectorized form

[Peter Dalgaard]

jgarcia at ija.csic.es wrote:
> Hi;
> It seems to me that has probably been asked in the past. But I cannot find
> the track.
>
> I usually need to extract elements from a list and contruct vector from
> them; e.g., to create a table. Perhaps there is a way to directly extract
> them without looping?
> Simple example:
>
>   
>> S.lst
>>     
> $sublist.1
> $sublist.1$age
> [1] 24.58719
>
> $sublist.1$weight
> [1] 60.82861
>
>
> $sublist.2
> $sublist.2$age
> [1] 32.39551
>
> $sublist.2$weight
> [1] 59.46347
>
> etc.
>
> I would like to extract, e.g.,  directly all weights element from each
> sublist without looping. I  know it is possible to do this as:
>
> unlist(S.lst)[paste("sublist.",1:length(S.lst),".weight",sep="")]
>
> but there is not some short-cut? something like
>
> S.lst[[1:length(S.lst)]]$weight ?
>
>   
I think this should do it:

sapply(S.lst, "[[", "weight")

-- 
   O__  ---- Peter Dalgaard             Øster Farimagsgade 5, Entr.B
  c/ /'_ --- Dept. of Biostatistics     PO Box 2099, 1014 Cph. K
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