[R] SQL/R

[Brian Diggs]

On 7/22/2010 5:01 AM, Allan Engelhardt wrote:
> There are so many ways....  Here is one:
>
> aggregate(v ~ u, data=X, function(...) length(unique(...)))
> # u v
> # 1 T1 2
> # 2 T2 1
>
> Hope this helps

Here is one other way, using the plyr package (which is very good for 
taking a data structure (data.frame, list, array), pulling it apart by 
some criteria, doing something on each of the parts, and putting the 
results back together):

library("plyr")
ddply(X, .(u), function(x) {length(unique(x$v))})
#   u V1
#1 T1  2
#2 T2  1


> Allan.
>
> On 22/07/10 12:52, Gildas Mazo wrote:
>> Dear R users,
>>
>> I want to aggregate data in the following way:
>>
>> ###
>>
>> X<- data.frame(u = c("T1","T1","T1","T2"), v=c("a","a","b","a"))
>> X
>> library(sqldf)
>> sqlOut<- sqldf("select count(distinct(v)) from X group by u")
>> sqlOut
>>
>> ###
>>
>> Now I want to get the same result without using SQL. How can I achieve
>> that ?
>>
>> Thanks for your help,
>>
>> Gildas
>>
>> ______________________________________________
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>> PLEASE do read the posting guide
>> http://www.R-project.org/posting-guide.html
>> and provide commented, minimal, self-contained, reproducible code.
>>
>


-- 
--
Brian Diggs
Senior Research Associate, Department of Surgery, Oregon Health & 
Science University