On Mar 30, 2012, at 3:38 AM, Milan Bouchet-Valat wrote:
Le jeudi 29 mars 2012 à 09:49 -0500, Yongsuhk Jung a écrit :
Dear Members of the R-Help,
While using a R function - 'aggregate' that you developed, I become
to have
a question.
In that function,
aggregate(x, by, FUN, ..., simplify = TRUE)
I was wondering about what type of FUN I should write if I want to
get "the
most frequent value of the subgroup" as a summary statistics of the
subgroups.
I will appreciate if I can get your idea on this issue.
It would have been better if you had provided a sample data as asked
by
the posting guide.
How TRUE.
Anyway, here's a possibility:
df <- data.frame(a=rep(1:3, 2), b=c(1, 2, 2, 1, 1, 2))
df
a b
1 1 1
2 2 2
3 3 2
4 1 1
5 2 1
6 3 2
aggregate(df$a, list(df$b), function(x) max(table(x)))
Group.1 x
1 1 2
2 2 2
Prompted by the obvious error in that solution (since the mode of b==1
is 1 and the mode of b==2 is 3) I thought I would take my untested
code strategy and fix it as well, now that an example was "on the
table" for discussion:
> aggregate(df1[1], by=df1[2], FUN=function(x){ tbl <- table(x);
return( dimnames(tbl)[[1]][ which.max(tbl)] )
} )
b a
1 1 1
2 2 3
( The modal values are in the "a" column.)
--
David Winsemius, MD
West Hartford, CT
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