[R] how to search a list that contains multiple dissimilarvectors?

[Gerrit Eichner]

Hi, Eric,

as a quick hack, does

spots <- sapply( alist,
                  function( listcomp)
                   which( listcomp == value.to.look.for) )

spots[ sapply( spots, length) == 0] <- NULL

do what you want?


Regards  --  Gerrit


On Thu, 28 Mar 2013, Eric Rupley wrote:

>
> Dear All,
>
> This is a simple question, but I'm stumped about the simplest way to 
> search a list object such as the following:
>
> This randomish snippet:
>
> n <- c(round(runif(round(runif(1,1,10),0),1,10),0))
> alist <- new("list")
> for (i in seq_along(n)) {
> 	alist[[i]] <- c(round(runif(round(runif(1,1,10),0),1,10),0))
> }
> names(alist) <- sample(letters[1:length(n)])
> rm(n);c(alist)
>
>
> ...produces something like this:
>
> $d
> [1] 4
>
> $b
> [1] 3 5 3
>
> $a
> [1]  2  5  7  3 10  3  4  9  9
>
> $c
> [1]  6  3  7  4  5 10  8 10  3
>
> My question is how does one search the list for a given value, in a most compressed set of commands, in order two return two separate indices: a) the index of the list element(s) containing the value, and b) the index of the matching value(s) within the vector.
>
> Right now, I'm writing cumbersome loops to iterate though the elements, but there must be a simple, effective method to which I have not found a reference.
>
> Many thanks in advance, and apologies if I have overlooked a reference passage.
> Best,
> Eric
>
> --
> Eric Rupley
> University of Michigan, Museum of Anthropology
> 1109 Geddes Ave, Rm. 4013
> Ann Arbor, MI 48109-1079
>
>
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