Thank you, David
Here is an example :
Z=matrix(rnorm(20), nrow=4)
index=replicate(4, sample(1:5, 3))
P=4
tmpr=list()
for (i in 1:P)
{
tmp = Z[i,index[,i]]
tmpr[[i]]=tmp
}
So, I am trying to pull out the values in Z for each row, but now I only
want to pull out the values indexed by the matrix "index"
And, since I have large P, so I would like to avoid loop.
Any quick way to do this ?
Thanks again!!
Carrie
On Thu, Feb 4, 2010 at 10:39 PM, David Winsemius <dwinsem...@comcast.net>wrote:
>
> On Feb 4, 2010, at 9:51 PM, Carrie Li wrote:
>
> Dear R-helpers ,
>>
>> I have a simple loop as follows, however, to be more efficient, I would
>> like
>> to use any apply functions (tapply, I suppose)
>> But how can I do this ? I am not very clear about this.
>>
>> # Z is a P * Q matrix
>> # so for each row of Z, I would like to pull out only some of the
>> elements,
>> and save as a separate matrix under a list
>> # index is a vector with length smaller than Q, but the index could be
>> different for each row of Z.
>>
>
> An example would help. Sounds like you need a list structure to hold the
> index and I don't see that you have constructed one.
>
>
>> for (i in 1:P)
>> {
>> tmp = matrix(Z[i, index], nrow=1)
>>
>
> Seems as though you would need to "index" in a verb sense (with "i") the
> index (in a noun sense) structure. Might be better to call it "idx".
> Perhaos
>
> tmp = matrix(Z[i, index[[i]] ], nrow=1) # the nrow=1 appears superfluous
>
>
> tmpr[[i]]=tmp
>> }
>>
>>
> any help is highly appreciated!!
>>
>> Thank you all
>>
>> Carrie
>>
>> [[alternative HTML version deleted]]
>>
>> ______________________________________________
>> R-help@r-project.org mailing list
>> https://stat.ethz.ch/mailman/listinfo/r-help
>> PLEASE do read the posting guide
>> http://www.R-project.org/posting-guide.html
>> and provide commented, minimal, self-contained, reproducible code.
>>
>
> David Winsemius, MD
> Heritage Laboratories
> West Hartford, CT
>
>
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