[R] how to simplify a data.frame and add the counts of duplicate rows as a new column

[Simone Gabbriellini]

many thanks, this is really a great solution!

best,
Simone

Il giorno 02/mar/2011, alle ore 16.22, Scott Chamberlain ha scritto:

> see package plyr, especially the function ddply(), eg.., in your case:
> 
> ddply(dataframe, .(columnA, columnB), summarise, 
> 	columnC = length(columnB)
> )
> 
> Scott
> On Wednesday, March 2, 2011 at 9:10 AM, Simone Gabbriellini wrote:
> 
>> Hello List,
>> 
>> I would like to simplify a data.frame like this
>> 
>> columnA	columnB
>> user10	 proj12
>> user10	 proj19
>> user10	 proj12
>> 
>> into something like:
>> 
>> columnA	columnB	columnC
>> user10	 proj12	 2
>> user10	 proj19	 1
>> 
>> I know unique() can simplify the data.frame, but how to count and store the duplicates?
>> 
>> thanks in advance for any help.
>> 
>> best regards,
>> Simone
>> 
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>