[R] A question on operation on list

David Winsemius dwinsemius at comcast.net
Wed Jul 22 23:43:56 CEST 2009


On Jul 22, 2009, at 5:07 PM, megh wrote:

>
> Thanks for your suggestions. I need one more thing :
>
> x = y = vector("list")
> for (i in 1:5) x[[i]] = rnorm(2);  y[[i]] = rnorm(2)
>
> Here I want to get t(x[[i]]) %*% y[[i]] for each i. Can anyone  
> please help
> me?
>

?lapply


> Regards,
>
>
>
> Jorge Ivan Velez wrote:
>>
>> Hi megh,
>> Perhaps?
>>
>> # Data
>> x = vector("list")
>> for (i in 1:5) x[[i]] = rnorm(2)
>>
>> # 2x2 matrices
>> res <- lapply(x, function(a) a %*% t(a) )
>> res
>>
>> # Funcion from ?Reduce
>> add <- function(x) Reduce("+", x)
>>
>> # Summing up!
>> add(res)
>>
>> See ?lapply and ?Reduce for more information.
>>
>> HTH,
>>
>> Jorge
>>
>>
>> On Wed, Jul 22, 2009 at 3:18 PM, megh <megh700004 at yahoo.com> wrote:
>>
>>>
>>> Hi,
>>> I have created a list object like that :
>>> x = vector("list")
>>> for (i in 1:5) x[[i]] = rnorm(2)
>>> x
>>>
>>> Now I want to do two things :
>>> 1. for each i, I want to do following matrix calculation :  
>>> t(x[[i]]) %*%
>>> x[[i]] i.e. for each i, I want to get a 2x2 matrix
>>> 2. Next I want to get  x[[1]] + x[[2]] +....
>>>
>>> I did following : res=vector("list"); res = sapply(x, function(i)
>>> t(x[[i]])
>>> %*% x[[i]])
>>> However above syntax is not giving desired result. Any suggestion  
>>> please?
>>>
>>> --
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>>> Sent from the R help mailing list archive at Nabble.com.
>>>
>>> ______________________________________________
>>> R-help at 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.
>>>
>>
>> 	[[alternative HTML version deleted]]
>>
>> ______________________________________________
>> R-help at 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.
>>
>>
>
> -- 
> View this message in context: http://www.nabble.com/A-question-on-operation-on-list-tp24612796p24614641.html
> Sent from the R help mailing list archive at Nabble.com.
>
> ______________________________________________
> R-help at 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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