[R] Compare rows of two matrices

[Liaw, Andy]

Here's one way:

> idx <- which(! paste(l1, collapse=":") %in% paste(l2, collpase=":"))
> l1[idx,]
row col 
  2   1 

Andy

> From:  TEMPL Matthias
> 
> Hello,
> 
> #I have two matrices, eg.:
> 
> y <-  matrix( c(20,  NA,  NA,  45,  50,  19,  32, 101,  10,  
> 22,  NA,  NA,  80,  49,  61, 190), ncol=4 )
> x <-  matrix( c(20,  NA,  NA,  NA,  50,  19,  32, 101,  10,  
> 22,  NA,  NA,  80,  49,  61, 190), ncol=4 )
> 
> #Whereas x contains all NA´s from y plus some additional NA´s.
> #I want to find the index of these additional NA´s. I think, 
> there must be a very easy way to do this.
> 
> #Here are the indices of NA´s in x and y:
> l1 <- which(is.na(x), arr.ind=TRUE)
> l2 <- which(is.na(y), arr.ind=TRUE)
> 
> #> l1
> #     [,1] [,2]
> #[1,]    2    1
> #[2,]    3    1
> #[3,]    4    1
> #[4,]    3    3
> #[5,]    4    3
> 
> #> l2
> #     row col
> #[1,]   2   1
> #[2,]   3   1
> #[3,]   3   3
> #[4,]   4   3
> 
> #Now I want to find a matrix, which includes the values of 
> l1, without the rows of l2, 
> #which has equal entities (the index of the additional NA´S).
> #In this example the result should be row 3 of l1 with the 
> values 4 and 1.
> #The following code works, but I think there must be a much 
> more elegant way to do this.
> 
> l3 <- l1
> l3 <- cbind( l1, rep(0, nrow(l1)) )
> num <- 1
>    
> for( i in 1:nrow(l1) ){
>   for( j in 1:nrow(l2) ){
>     if( l1[i,1] == l2[j,1] & l1[i,2] == l2[j,2]){
>       l3[i,3] <- 1
>     }
>   }
> }
> 
> l4 <- l3[l3[,3]==0, c(1,2)]
> 
> #> l4
> #row col 
> #  4   1  
> 
> I have often such problems like this and I assume, that other 
> people have similar tasks.
> My question is: Does anybody know a function in one package, 
> which compares rows of two matrices like this or have anybody 
> an idea to do this in a much more elegant way"? 
> 
> Thank you very much,
> Matthias
> 
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