tally {dplyr}R Documentation

Count/tally observations by group

Description

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. If the data is already grouped, count() adds an additional group that is removed afterwards.

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 = NULL, sort = FALSE, name = "n")

count(x, ..., wt = NULL, sort = FALSE, name = "n",
  .drop = group_by_drop_default(x))

add_tally(x, wt, sort = FALSE, name = "n")

add_count(x, ..., wt = NULL, sort = FALSE, name = "n")

Arguments

x

a tbl() to tally/count.

wt

(Optional) If omitted (and no variable named n exists in the data), will count the number of rows. If specified, will perform a "weighted" tally by summing the (non-missing) values of variable wt. A column named n (but not nn or nnn) will be used as weighting variable by default in tally(), but not in count(). This argument is automatically quoted and later evaluated in the context of the data frame. It supports unquoting. See vignette("programming") for an introduction to these concepts.

sort

if TRUE will sort output in descending order of n

name

The output column name. If omitted, it will be n.

...

Variables to group by.

.drop

see group_by()

Value

A tbl, grouped the same way as x.

Note

The column name in the returned data is given by the name argument, set to "n" by default.

If the data already has a column by that name, the output column will be prefixed by an extra "n" as many times as necessary.

Examples

# tally() is short-hand for summarise()
mtcars %>% tally()
mtcars %>% group_by(cyl) %>% tally()
# count() is a short-hand for group_by() + tally()
mtcars %>% count(cyl)
# Note that if the data is already grouped, count() adds
# an additional group that is removed afterwards
mtcars %>% group_by(gear) %>% count(carb)

# 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)

# Change the name of the newly created column:
species <-
 starwars %>%
 count(species, homeworld, sort = TRUE, name = "n_species_by_homeworld")
species
species %>%
 count(species, sort = TRUE, name = "n_species")

# add_count() is useful for groupwise filtering
# e.g.: show details for species that have a single member
starwars %>%
  add_count(species) %>%
  filter(n == 1)

[Package dplyr version 0.8.5 Index]