dplyr count number of one specific value of variable

Question

Say I have a dataset like this:

id <- c(1, 1, 2, 2, 3, 3)
code <- c(\"a\", \"b\", \"a\", \"a\", \"b\", \"b\")
dat <- data.frame(id, code)

Answer 1

Try the following instead:

library(dplyr)
dat %>% group_by(id) %>%
  summarise(cip.completed= sum(code == "a"))

Source: local data frame [3 x 2]
    id cip.completed
  (dbl)         (int)
1     1             1
2     2             2
3     3             0

This works because the logical condition code == a is just a series of zeros and ones, and the sum of this series is the number of occurences.

Note that you would not necessarily use dplyr::count inside summarise anyway, as it is a wrapper for summarise calling either n() or sum() itself. See ?dplyr::count. If you really want to use count, I guess you could do that by first filtering the dataset to only retain all rows in which code==a, and using count would then give you all strictly positive (i.e. non-zero) counts. For instance,

dat %>% filter(code==a) %>% count(id)

Source: local data frame [2 x 2]

     id     n
  (dbl) (int)
1     1     1
2     2     2