[R] sapply problem

[Weiwei Shi]

> c <- apply(b, c(1,2), unlist)
> c
     A B C
[1,] 1 2 3
[2,] 4 5 6
> class(c[1,1])
[1] "numeric"


On 12/14/06, Joerg van den Hoff <j.van_den_hoff at fz-rossendorf.de> wrote:
> I have encountered the following problem: I need to extract from
> a list of lists equally named compenents who happen to be 'one row'
> data frames. a trivial example would be:
>
> a <- list(list(
> df = data.frame(A = 1, B = 2, C = 3)), list(df = data.frame(A = 4,B = 5,C = 6)))
>
> I want the extracted compenents to fill up a matrix or data frame row by row.
> the obvious thing to do seems:
>
> b <- sapply(a, "[[", "df")
> b <- t(b)
>
> now `b' looks all right:
>
> b
> class(b)
>
> but it turns out that all elements in this matrix are one element lists:
>
> class(b[1,1])
>
> which prevents any further standard processing of `b' (like `colMeans', e.g.)
>
> question 1: is their a straightforward way to enforce that `b' contains
> simple numbers as elements right from the start (instead of something like
> apply(b, 1:2, "class<-", "numeric") afterwards)?
>
> question 2: should not sapply do this further 'simplification' anyway in a situation
> like this (matrix elements turn out to be one-element lists)?
>
> regards
>
> joerg
>
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-- 
Weiwei Shi, Ph.D
Research Scientist
GeneGO, Inc.

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