[R] Selecting rows that are the same in separate data frames

[ppaarrkk]

Thanks for reply.

What I want is the equivalent of this :

xxx = 1:10
which(xxx %in% c(2,5))


.......but where there is more than one criterion for matching.


which (b %in% a) in the code I included does nothing (not surprisingly).

I'm not sure that I can use merge, because I want the whole of a, but to
mark those rows which are also in b. If I do merge ( a,b ),  I just get b.
If I do merge ( a,b, all.x =TRUE), I get a.




bartjoosen wrote:
> 
> I'm not sure what you want, but take a look at ?merge and %in%
> 
> 
> ppaarrkk wrote:
>> 
>> I want to compare two matrices or data frames and select or get an index
>> for those rows which are the same in both. I have tried the following :
>> 
>> 
>> 
>> 
>> 
>> 
>> a = matrix ( 1:10, ncol = 2 )
>> a
>> 
>> b = matrix ( c ( 2,3,4,7,8,9 ), ncol = 2 )
>> b
>> 
>> a[a==b]
>> 
>> 
>> 
>> 
>> 
>> 
>> a = as.data.frame ( matrix ( 1:10, ncol = 2 ) )
>> a
>> 
>> b = as.data.frame ( matrix ( c ( 2,3,4,7,8,9 ), ncol = 2 ) )
>> b
>> 
>> a[a==b]
>> 
>> 
>> 
>> 
>> 
>> 
>> 
>> 
>> Any ideas please.
>> 
>> 
>> Thanks.
>> 
>> 
>> Simon Parker
>> Imperial College
>> 
>> 
> 
> 

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