Re: [R] matrix indexing in 'for' loop?

[govindas]

Thank you both for your suggestions. I have another question - is there a 
specific way to access the individual elements of a 'list' variable? i.e. 

dmi = matrix(rnorm(20),4,5)
soi = matrix(rnorm(20),4,5)
pe = matrix(rnorm(20),4,5)
y <- list(dmi, soi, pe)

y[[1]]   gives
[,1]       [,2]       [,3]       [,4]       [,5]
[1,] -0.54463900  1.6732445 -0.3807847 -1.0460530 -0.8142748
[2,] -0.49654004 -0.9634258  0.9074139 -0.1576030 -1.2268558
[3,] -1.61835766 -0.4240122  0.3626670  0.7182964  0.1576446
[4,] -0.06313983  0.6743465 -1.9897107  0.8027337 -1.4372131

But, I am interested in accessing the 1st column of 'dmi' matrix here - not as 
dmi[,1] but in terms of 'y'. Is it possible with 'list' function or something 
else?

Thanks again. 

-- 
Regards,
Maha
Graduate Student
Department of Geography
Michigan State University
 Quoting Liviu Andronic <landronim...@gmail.com>:

> On Wed, Dec 22, 2010 at 2:57 AM, Phil Spector 
> <spec...@stat.berkeley.edu> wrote:
>> To make your loop work, you need to learn about the get function.
>> I'm not going to give you the details because there are better
>> approaches available.
>> First, let's make some data that will give values which can be verified.
>>  (All the correlations of the data you created
>> are exactly equal to 1.)  And to make the code readable, I'll
>> omit the ts.m prefix.
>>
>>> set.seed(14)
>>> dmi = matrix(rnorm(20),4,5)
>>> soi = matrix(rnorm(20),4,5)
>>> pe = matrix(rnorm(20),4,5)
>>> allmats = list(dmi,soi,pe)
>>
>> Since cor.test won't automatically do the tests for all columns
>> of a matrix, I'll write a little helper function:
>>
>>> gettests = function(x)apply(x,2,function(col)cor.test(pe[,2],col)
>>> tests = lapply(allmats,gettests)
>>
>> Now tests is a list of length 2, with a list of the output from
>> cor.test for the five columns of the each matrix with pe[,2]
>> (Notice that in your program you made no provision to store the results
>> anywhere.)
>>
>> Suppose you want the correlations:
>>
>>> sapply(tests,function(x)sapply(x,function(test)test$estimate))
>>
>>           [,1]       [,2]
>> cor  0.12723615  0.1342751
>> cor  0.07067819  0.6228158
>> cor -0.28761533  0.6218661
>> cor  0.83731828 -0.9602551
>> cor -0.36050836  0.1170035
>>
>> The probabilities for the tests can be found similarly:
>>
>>> sapply(tests,function(x)sapply(x,function(test)test$p.value))
>>
>>          [,1]       [,2]
>> [1,] 0.8727638 0.86572490
>> [2,] 0.9293218 0.37718416
>> [3,] 0.7123847 0.37813388
>> [4,] 0.1626817 0.03974489
>> [5,] 0.6394916 0.88299648
>>
> Hmisc already provides a function for doing this, rcorr(). Try to
> compute correlations using Rcmdr for an example.
>
> Regards
> Liviu
>
>
>> (Take a look at the "Values" section in the help file for cor.test
>> to get the names of other quantities of interest.)
>>
>> The main advantage to this approach is that if you add more matrices
>> to the allmats list, the other steps automaticall take it into account.
>>
>> Hope this helps.
>>                                        - Phil Spector
>>                                         Statistical 
>> Computing Facility
>>                                         Department of 
>> Statistics
>>                                         UC Berkeley
>>                                         
>> spec...@stat.berkeley.edu
>>
>>
>>
>>
>>
>> On Tue, 21 Dec 2010, govin...@msu.edu wrote:
>>
>>>
>>>
>>> Hi,
>>>
>>> I am having trouble with matrices. I?have 2 matrices as given below, and I
>>> am interested in using these matrices inside "for" loops used to calculate
>>> correlations. I am creating a list with the names of the matrices assuming
>>> this list could be indexed inside the 'for' loop to retrieve the matrix
>>> values. But, as expected the code throws out an error. Can someone 
>>> suggest a
>>> better way to call these matrices inside the loops?
>>>
>>> ts.m.dmi <- matrix(c(1:20), 4, 5)
>>> ts.m.soi <- matrix(c(21:40), 4, 5)
>>> ts.m.pe <- matrix(c(21:40), 4, 5)
>>>
>>> factors <- c("ts.m.dmi", "ts.m.soi")
>>> for (j in 0:1){
>>> y <- factors[j+1]
>>>
>>> for (i in 1:5){
>>>
>>> cor.pe.y <- cor(ts.m.pe[,2], y[,i])
>>> ct.tst <- cor.test(ts.m.pe[,2], y[,i])
>>> }
>>> }
>>>
>>> Thanks for your time.
>>>
>>> --
>>> Regards,
>>> Maha
>>> Graduate Student
>>>        [[alternative HTML version deleted]]
>>>
>>>
>>
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>>
>
>
>
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