R help - Aug 2007 - how to collapse a list of 1 column matrix to a matrix?

Hi, 

I encounter a situation where I have a list whose element is a column matrix.
Says,

$'1'
[,1]
1
2
3

$'2'
[,1]
4
5
6

Is there fast way to collapse the list into a matrix like a cbind operation in
this case? Meaning, the result should be a matrix that looks like:

      [,1]  [,2]
[1,]    1      4
[2,]    2      5
[3,]    3      6

I can loop through all elements and do cbind manually. But I think there must be
a simpler way that I don't know. Thank you.

- adschai

[adschai at optonline.net]
>I encounter a situation where I have a list whose element is a column 
>matrix. Says,
>$'1'
>[,1]
>1
>2
>3
>$'2'
>[,1]
>4
>5
>6
>Is there fast way to collapse the list into a matrix like a cbind 
>operation in this case? Meaning, the result should be a matrix that 
>looks like: 
>      [,1]  [,2]
>[1,]    1      4
>[2,]    2      5
>[3,]    3      6
>I can loop through all elements and do cbind manually. But I think 
>there must be a simpler way that I don't know. Thank you.
The "do.call" function is the R equivalent of the "apply"
from many
other languages.  I guess that, in R, "apply" was already taken :-)
For example:
> a = list(x=matrix(1:3, 3, 1), y=matrix(4:6, 3, 1))
> a
$x
     [,1]
[1,]    1
[2,]    2
[3,]    3

$y
     [,1]
[1,]    4
[2,]    5
[3,]    6
> do.call(cbind, a)
     [,1] [,2]
[1,]    1    4
[2,]    2    5
[3,]    3    6


-- 
Fran?ois Pinard   http://pinard.progiciels-bpi.ca

Try this:

L <- list(`1` = matrix(1:4, 4), `2` = matrix(5:8, 4))
sapply(L, c)

Note that the list component names are kept as column names in the result


On 8/19/07, adschai at optonline.net <adschai at optonline.net>
wrote:
> Hi,
>
> I encounter a situation where I have a list whose element is a column
matrix. Says,
>
> $'1'
> [,1]
> 1
> 2
> 3
>
> $'2'
> [,1]
> 4
> 5
> 6
>
> Is there fast way to collapse the list into a matrix like a cbind operation
in this case? Meaning, the result should be a matrix that looks like:
>
>      [,1]  [,2]
> [1,]    1      4
> [2,]    2      5
> [3,]    3      6
>
> I can loop through all elements and do cbind manually. But I think there
must be a simpler way that I don't know. Thank you.
>
> - adschai
>
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