[R] tapply to data.frame or matrix

[arun]

Hi,
Here's another way:
testagg<-aggregate(colnames(test),list(test.ind),function(x) test[,x])
list(unlist(testagg[,2][1]),unlist(testagg[,2][2]))
#[[1]]
#0.V11 0.V12 0.V13 0.V14 0.V21 0.V22 0.V23 0.V24 
    1     2     3     4     5     6     7     8 

#[[2]]
#1.V31 1.V32 1.V33 1.V34 1.V41 1.V42 1.V43 1.V44 1.V51 1.V52 1.V53 1.V54 
 #   9    10    11    12    13    14    15    16    17    18    19    20 
A.K.




----- Original Message -----
From: Rui Barradas <ruipbarradas at sapo.pt>
To: Jannis <bt_jannis at yahoo.de>
Cc: r-help <r-help at r-project.org>
Sent: Tuesday, September 4, 2012 11:30 AM
Subject: Re: [R] tapply to data.frame or matrix

Hello,

Here's a way.

test <- as.data.frame(matrix(1:20, ncol = 5, nrow=4))
test.ind <- c(1,1,2,2,2)

lapply(split(colnames(test), test.ind), function(x) unlist(test[, x]))

Hope this helps,

Rui Barradas
Em 04-09-2012 15:40, Jannis escreveu:
> Dear R users,
>
>
> imagine i have a dataframe and an indexing vector with the length of the
> amount of columns of the dataframe. Is there any convenient way to
> combine the colums of the dataframe into vectors (or straight away apply
> fundtions to these subsets) according to the indexing vector in a
> similar manner to the tapply function?
>
> For example, in the follwoing case, I would like to combine columns 1
> and two into one vector, and columns 3-4 into another:
>
> test     = as.data.frame(matrix(1:20, ncol = 5, nrow=4))
> test.ind =c(1,1,2,2,2)
>
>
> Thanks a lot!
> Jannis
>
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