[R] Remove rows in a matrix that match rows in another matrix

[David Winsemius]

On Dec 19, 2009, at 11:11 PM, Raymond Danner wrote:

> Dear R Community,
>
> The following seems like a simple problem, but I've been stuck on it  
> for
> some time, with no luck using matching or subsetting functions.  I'm  
> trying
> to remove the rows from a large matrix that match rows in another  
> large
> matrix.  A (small scale) example:
>
> col1<-c("A", "B", "C", "D")
> col2<-c("A", "B", "C", "D")
> m1<-cbind(col1, col2)
> col3<-c("B", "C", "D")
> col4<-c("B", "C", "z")
> m2<-cbind(col3, col4)
>
> Any ideas on how to get the following matrix?
>     [,1] [,2]
> [1,] "A"  "A"
> [2,] "D"  "D"
>

I have an idea but I don't claim it to be the most elegant"

apply(m1, 1, function(x) max( apply(m2, 1, function(y) all.equal(x, y,  
check.attributes=FALSE)) ) ) != "TRUE"
[1]  TRUE FALSE FALSE  TRUE

So....using logical indexing...

m1[apply(m1, 1, function(x) max(    # max(c(TRUE,FALSE))==TRUE
               apply(m2, 1, function(y)   # now cycle through all of  
2nd mtx
                   all.equal(x, y, check.attributes=FALSE)) ) ) !=  
"TRUE" , ]

Last logical test "inverts" the result so you get the non-matched rows.

      col1 col2
[1,] "A"  "A"
[2,] "D"  "D"

all.equal is set up to allow ignoring the attributes (col names)  
whereas identical did not appear to allow that

> Thanks very much in advance,
> Ray
>
>
> 	[[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.

David Winsemius, MD
Heritage Laboratories
West Hartford, CT