[R-lang] apply through a list

[Andy Fugard]

Here's a slow solution to your average problem, which I think works.   
Would it generalise?  I guess using a for loop is a terribly bad  
idea, especially if you've got a heap of matrices, though.

listmatapply(l,f) takes a list of matrices, l, and a function, f,  
mapping two matrices to a matrix.

Andy

======================================================================== 
======

M1 <- matrix( 1:4, nrow=2, ncol=2)
M2 <- matrix( 5:8, nrow=2, ncol=2)
M3 <- matrix( 9:12, nrow=2, ncol=2)
M4 <- matrix( 13:16, nrow=2, ncol=2)
M5 <- matrix( 17:20, nrow=2, ncol=2)

L <- list( M1, M2, M3, M4, M5 )

dim(M1)

listmatapply <- function(l,f) {
   tempres <- f(l[[1]], l[[2]])
   i <- 3
   while ( i <= length(L) ) {
     	tempres <- f(tempres, l[[i]])
     	i <- i + 1
     	tempres
   }
   tempres
}

averagel <- function(L) {
    listmatapply(L,function(x,y) { x + y}) / length(L)
}

averagel(L)



On 16 May 2007, at 21:43, Michael Cysouw wrote:

> unfortunatly not: "lapply" applies a function to every element in a
> list - I am trying to do something with a recurrent part of each
> element in the list.
>
> For example:
>
> M1 <- matrix( 1:4, nrow=2, ncol=2)
> M2 <- matrix( 5:8, nrow=2, ncol=2)
>
> L <- list( M1, M2 )
>
> How do I apply a function to every position in the matrix through all
> matrices, say take the average. Expected result:
>
>       [,1] [,2]
> [1,]    3    5
> [2,]    4    6
>
> best
> michael
>
>
> On 16 May 2007, at 21:18, Joan Bresnan wrote:
>
>> Are you looking for lapply?
>> lapply                 package:base                 R Documentation
>>
>> Apply a Function over a List or Vector
>>
>> Description:
>>
>>     'lapply' returns a list of the same length as 'X', each  
>> element of
>>     which is the result of applying 'FUN' to the corresponding  
>> element
>>     of 'X'.
>>
>>     'sapply' is a "user-friendly" version of 'lapply' by default
>>     returning a vector or matrix if appropriate.
>>
>>     'replicate' is a wrapper for the common use of 'sapply' for
>>     repeated evaluation of an expression (which will usually involve
>>     random number generation).
>>
>> Usage:
>>
>>     lapply(X, FUN, ...)
>>
>>     sapply(X, FUN, ..., simplify = TRUE, USE.NAMES = TRUE)
>>
>>
>>
>>
>> On 5/16/07, Michael Cysouw <cysouw at eva.mpg.de> wrote:
>>> a general question, not specific to linguistics...
>>>
>>> I have a (large) set of same-size matrices M1,M2,M3,... which I
>>> stored in a list. How do I apply a function over the same  
>>> position of
>>> all matrices? For example, take the sum M1+M2+M3+...
>>>
>>> I have not found any "apply" like variant that would do the trick.
>>> Any suggestions?
>>>
>>> best
>>> michael
>>>
>>>
>>> —————————————————————————
>>> Michael Cysouw
>>>
>>> Department of Linguistics
>>> Max Planck Institute for Evolutionary Anthropology
>>> Deutscher  Platz 6
>>> D-04103 Leipzig
>>>
>>> Room: U 1.14
>>>
>>> phone:    +49 (0) 341 35 50 316
>>> fax:          +49 (0) 341 35 50 333
>>> home:       +49 (0) 341 22 59 488
>>> mobile:      +49 (0) 172 18 33 507
>>> e-mail:       cysouw at eva.mpg.de
>>> homepage:  http://www.eva.mpg.de/~cysouw/
>>> —————————————————————————
>>>
>>>
>>>
>>> _______________________________________________
>>> R-lang mailing list
>>> R-lang at ling.ucsd.edu
>>> https://ling.ucsd.edu/mailman/listinfo.cgi/r-lang
>>>
>>
>>
>> -- 
>> Joan Bresnan
>> Stanford University
>> http://www.stanford.edu/~bresnan/
>
>
> _______________________________________________
> R-lang mailing list
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>


--
Andy Fugard, Postgraduate Research Student
Psychology (Room F15), The University of Edinburgh,
   7 George Square, Edinburgh EH8 9JZ, UK
Mobile: +44 (0)78 123 87190   http://www.possibly.me.uk