tally
Count/tally observations by group
tally() is a convenient wrapper for summarise that will either call
n() or sum(n) depending on whether you're tallying
for the first time, or re-tallying. count() is similar but calls
group_by() before and ungroup() after.
add_tally() adds a column n to a table based on the number
of items within each existing group, while add_count() is a shortcut that
does the grouping as well. These functions are to tally()
and count() as mutate() is to summarise():
they add an additional column rather than collapsing each group.
Usage
tally(x, wt, sort = FALSE)count(x, ..., wt = NULL, sort = FALSE)
add_tally(x, wt, sort = FALSE)
add_count(x, ..., wt = NULL, sort = FALSE)
Arguments
- x
a
tbl()to tally/count.- wt
(Optional) If omitted (and no variable named
nexists in the data), will count the number of rows. If specified, will perform a "weighted" tally by summing the (non-missing) values of variablewt. A column namedn(but notnnornnn) will be used as weighting variable by default intally(), but not incount(). This argument is automatically quoted and later evaluated in the context of the data frame. It supports unquoting. Seevignette("programming")for an introduction to these concepts.- sort
if
TRUEwill sort output in descending order ofn- ...
Variables to group by.
Value
A tbl, grouped the same way as x.
Note
The column name in the returned data is usually n, even if you
have supplied a weight.
If the data already already has a column named n, the output column
will be called nn. If the table already has columns called n and nn
then the column returned will be nnn, and so on.
There is currently no way to control the output variable name - if you
need to change the default, you'll have to write the summarise()
yourself.
Examples
# NOT RUN {
# tally() is short-hand for summarise()
mtcars %>% tally()
# count() is a short-hand for group_by() + tally()
mtcars %>% count(cyl)
# add_tally() is short-hand for mutate()
mtcars %>% add_tally()
# add_count() is a short-hand for group_by() + add_tally()
mtcars %>% add_count(cyl)
# count and tally are designed so that you can call
# them repeatedly, each time rolling up a level of detail
species <- starwars %>% count(species, homeworld, sort = TRUE)
species
species %>% count(species, sort = TRUE)
# add_count() is useful for groupwise filtering
# e.g.: show only species that have a single member
starwars %>%
add_count(species) %>%
filter(n == 1)
# }