[R] adding matrices with common column names

[Nutter, Benjamin]

Shucks, Dimitris beat me to it.  And his code is a bit more elegant than
mine.  But since I did the work I may as well post it, right?

This version incorporates a couple of error checks to make sure all your
arguments are matrices with the same number of rows.

add.by.name <- function(...){
  args <- list(...)
  
  mat.test <- sapply(args,is.matrix)
  if(FALSE %in% mat.test) stop("All arguments must be matrices")

  mat.row <- unique(sapply(args,nrow))
  if(length(mat.row)>1) stop("All matrices must have the same number of
rows")
  
  all.names <- unique(as.vector(sapply(args,colnames)))
  
  sum.mat <- matrix(0,nrow=mat.row,ncol=length(all.names))
  colnames(sum.mat) <- all.names

  for(i in 1:length(args)){
    tmp <- args[[i]]
    sum.mat[,colnames(tmp)] <- sum.mat[,colnames(tmp)] + tmp
  }

  return(sum.mat)
}

m1 <- matrix(1:20,ncol=4); colnames(m1) <- c("a","b","c","d")
m2 <- matrix(1:20,ncol=4); colnames(m2) <- c("b","c","d","e")
m3 <- matrix(1:20,ncol=4); colnames(m3) <- c("a","b","d","e")

add.by.name(m1,m2,m3)



-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org]
On Behalf Of Murali.MENON at fortisinvestments.com
Sent: Friday, March 27, 2009 9:25 AM
To: r-help at r-project.org
Subject: [R] adding matrices with common column names

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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