[R] adding matrices with common column names

[Dimitris Rizopoulos]

one approach is:

a <- matrix(1:20,ncol=4); colnames(a) <- c("a","b","c","d")
b <- matrix(1:20,ncol=4); colnames(b) <- c("b","c","d", "e")
cc <- matrix(1:10,ncol=2); colnames(cc) <- c("e","f")

f <- function (...) {
     mat.lis <- list(...)
     unq.cnams <- unique(unlist(lapply(mat.lis, colnames)))
     out <- matrix(0, nrow(mat.lis[[1]]), length(unq.cnams),
         dimnames = list(NULL, unq.cnams))
     for (i in seq_along(mat.lis)) {
         mm <- mat.lis[[i]]
         out[, colnames(mm)] <- out[, colnames(mm)] + mm
     }
     out
}

f(a, b)
f(a, cc)
f(a, b, cc)


I hope it helps.

Best,
Dimitris


Murali.MENON at fortisinvestments.com wrote:
> folks,
>  
> if i have three matrices, a, b, cc with some colnames in common, and i
> want to create a matrix which consists of the common columns added up,
> and the other columns tacked on, what's a good way to do it? i've got
> the following roundabout code for two matrices, but if the number of
> matrices increases, then i'm a bit stymied.
>  
>> a <- matrix(1:20,ncol=4); colnames(a) <- c("a","b","c","d") b <- 
>> matrix(1:20,ncol=4); colnames(b) <- c("b","c","d", "e")
>> cbind(a[,!(colnames(a) %in% colnames(b)), drop = FALSE],
>         a[,intersect(colnames(a),colnames(b))] +
> b[,intersect(colnames(a),colnames(b)), drop = FALSE],
>         b[,!(colnames(b) %in% colnames(a)), drop = FALSE])
>  
>      a  b  c  d  e
> [1,] 1  7 17 27 16
> [2,] 2  9 19 29 17
> [3,] 3 11 21 31 18
> [4,] 4 13 23 33 19
> [5,] 5 15 25 35 20
>  
> now, what if i had a matrix cc? i want to perform the above operation on
> all three matrices a, b, cc.
>  
>> cc <- matrix(1:10,ncol=2); colnames(cc) <- c("e","f")
> 
> i need to end up with:
> 
>      a  b  c  d  e  f
> [1,] 1  7 17 27 17  6
> [2,] 2  9 19 29 19  7
> [3,] 3 11 21 31 21  8
> [4,] 4 13 23 33 23  9
> [5,] 5 15 25 35 25 10
> 
> and, in general, with multiple matrices with intersecting colnames?
> 
> thanks,
> 
> murali
> 
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-- 
Dimitris Rizopoulos
Assistant Professor
Department of Biostatistics
Erasmus University Medical Center

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