[R] How to locate the difference from two data frames

[David Winsemius]

On Apr 8, 2010, at 9:47 AM, Jun Shen wrote:

> Dear David, Erik and Charles,
>
> Thank you for your input. Both mapply() and which() can do the job.  
> Just one
> exception. If there is a missing value as NA in the data frame "a"  
> and a
> data point (either numerical or character) in the corresponding  
> position of
> "b", then mapply() only returns NA for that position rather than  
> "FALSE",
> and which() cannot pick up that position either. Thanks again.


You seem to have changed the programming challenge from identification  
to replicating identical(). If so then you can get closer with  
wrapping isTRUE(all() around the mapply("==" , attributes( ...), ...)   
step,  and wrap the "==" call in isTRUE(all(.))

 > isTRUE(all(mapply("==", df1, df2)) )
[1] FALSE  since all(c(NA, TRUE, TRUE)) == NA and isTRUE(NA) == FALSE

-- 
David.


>
> Jun
>
> On Wed, Apr 7, 2010 at 10:46 PM, Charles C. Berry <cberry at tajo.ucsd.edu 
> >wrote:
>
>> On Wed, 7 Apr 2010, Jun Shen wrote:
>>
>> Dear all,
>>>
>>> I understand identical (a,b) will tell me if a and b are exactly  
>>> the same
>>> or
>>> not. But what if they are different, is there anyway to tell which
>>> element(s) are different? Thanks.
>>>
>>
>> which( a != b, arr.ind = TRUE)
>>
>> HTH,
>>
>> Chuck
>>
>>>
>>> Jun
>>>
>>>
>>>       [[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.
>>>
>>>
>> 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
>>
>>
>>
>
> 	[[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
West Hartford, CT