David,

Thanks for the suggestion. Now I have worked out a general solution.

Assume "a" and "b" are two data frames with same dimensions

1. Call identical(a,b) to get an overall assessment. If you get a FALSE
2. Call which(mapply(identical,unlist(a),unlist(b))==FALSE), you will get a
result like
    TIME5
     85
which means, the row 5 and the column with name "TIME" is different. This
also works for missing values. Thanks for everyone.

Jun Shen from Millipore

On Thu, Apr 8, 2010 at 9:08 AM, David Winsemius <dwinsemius@comcast.net>wrote:

>
> 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@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@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@tajo.ucsd.edu               UC San Diego
>>> http://famprevmed.ucsd.edu/faculty/cberry/  La Jolla, San Diego
>>> 92093-0901
>>>
>>>
>>>
>>>
>>        [[alternative HTML version deleted]]
>>
>> ______________________________________________
>> R-help@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
>
>

	[[alternative HTML version deleted]]

