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setdiff for data frames

4 messages · Charles C. Berry, G. Jay Kerns, Brian Ripley

G. Jay Kerns
# 
Hello,

I have been interested in setdiff() for data frames that operates
row-wise.  I looked in the documentation, mailing lists, etc., and
didn't find exactly the right thing.  Given data frames A, B with the
same columns, the goal is to extract the rows that are in A, but not
in B.  Of course, one can usually do setdiff(rownames(A), rownames(B))
but that is cheating.  :-)

I played around a little bit and came up with

setdiff.data.frame = function(A, B){
     g <-  function( y, B){
                 any( apply(B, 1, FUN = function(x)
identical(all.equal(x, y), TRUE) ) ) }
     unique( A[ !apply(A, 1, FUN = function(t) g(t, B) ), ] )
}

I am sure that somebody can do this a better/faster way... any ideas?
Any chance we could get a data.frame method for set.diff in future R
versions? (The notion of "set" is somewhat ambiguous with respect to
rows, columns, and entries in the data frame case.)


Jay


P.S. You can see what I'm looking for with

A <- expand.grid( 1:3, 1:3 )
B <- A[ 2:5, ]
setdiff.data.frame(A,B)





***************************************************
G. Jay Kerns, Ph.D.
Assistant Professor / Statistics Coordinator
Department of Mathematics & Statistics
Youngstown State University
Youngstown, OH 44555-0002 USA
Office: 1035 Cushwa Hall
Phone: (330) 941-3310 Office (voice mail)
-3302 Department
-3170 FAX
E-mail: gkerns at ysu.edu
http://www.cc.ysu.edu/~gjkerns/
Charles C. Berry
#
On Mon, 10 Dec 2007, G. Jay Kerns wrote:

            

      
      
      
    

        
setdiff.data.frame <-
    function(A,B) A[ !duplicated( rbind(B,A) )[ -seq_len(nrow(B))] , ]

This ignores rownames(A) which may not be what is wanted in every case.

HTH,

Chuck

            

      
      
      
    

        

      
      
    

        
Charles C. Berry                            (858) 534-2098
                                             Dept of Family/Preventive Medicine
E mailto:cberry at tajo.ucsd.edu	            UC San Diego
http://famprevmed.ucsd.edu/faculty/cberry/  La Jolla, San Diego 92093-0901

  
  


  


      

    

    

      
      

        
      

    

    

      
      

        


  

        

      Brian Ripley
    

    

      
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On Mon, 10 Dec 2007, Charles C. Berry wrote:

        

            

      
      
      
    

        
I was about to suggest using the approach taken by duplicated.data.frame, 
(which is to 'hash' the rows to a character vector) then call setdiff.
E.g.

a <- do.call("paste", c(A, sep = "\r"))
b <- do.call("paste", c(B, sep = "\r"))
A[match(setdiff(a, b),a), ]

Note that apply() is intended for matrices (not data frames) and the 
version given can do a horrendous amount of coercion, whereas the above 
does it only once.

            

      
      
      
    

        
No chance: if you have not found it in the archives, it is too rare a 
request.