a <- c(rep(1:2,3))
b <- c("A","A","B","B","B","B")
df <- data.frame(a,b)
> str(b)
chr [1:6] "A" "A" "B" "B" "B" "B"
a b
1 1 A
2 2 A
3 1 B
4 2 B
5 1 B
6 2 B
I want to group by variable a
and return the most frequent value of b
My desired result would look like
a b
1 1 B
2 2 B
In dplyr
it would be something like
df %>% group_by(a) %>% summarize (b = most.frequent(b))
I mentioned dplyr
only to visualize the problem.
The key is to start grouping by both a
and b
to compute the frequencies and then take only the most frequent per group of a
, for example like this:
df %>%
count(a, b) %>%
slice(which.max(n))
Source: local data frame [2 x 3]
Groups: a
a b n
1 1 B 2
2 2 B 2
Of course there are other approaches, so this is only one possible "key".