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