Good morning,
 
I am merging two datasets and I would like to save the non-matching rows
in a separate file.
The problem is how to retrieve the non-matching rows in R.  
 
Example:
 
DATASET A
code   nomi
  A1 Franco
  A2  Mario
  A3 Andrea
  A4 Sandro
  A5   Luca

DATASET B
code                book
 A1        Guerra e Pace
 A1       Storia di Roma
 A2   La coscienza di Zeno
 A4              Ivanhoe
 A1         I Malavoglia
 A2     Jude the obscure

when merging two rows are unmatched:
 
A3 Andrea
A5   Luca
 
And these are exactly the rows I would like to store in a separate
file/dataset.
 
I tried with: 
 
AM<-merge(A,B,all=TRUE)
A1<-AM[is.na(AM$book),]
 
to keep the rows with a NA value in the book column.
 
The problem is that this works in this particular case, but in real
situations I might have other NA values in the book column, not
resulting from the merge operation, but that are real missing values: in
such cases, with the is.na command I would retrieve also thiese unneeded
rows.
 
Can someone suggest a better strategy to tackle this problem?
 
Regards,
Filippo Biscarini
Wageningen University
The Netherlands

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