nest_count: Count observations in a nested data frame by group

In nplyr: A Grammar of Nested Data Manipulation

Count observations in a nested data frame by group

Description

nest_count() lets you quickly count the unique values of one or more variables within each nested data frame. nest_count() results in a summary with one row per each set of variables to count by. nest_add_count() is equivalent with the exception that it retains all rows and adds a new column with group-wise counts.

Usage

nest_count(.data, .nest_data, ..., wt = NULL, sort = FALSE, name = NULL)

nest_add_count(.data, .nest_data, ..., wt = NULL, sort = FALSE, name = NULL)

Arguments

.data	A data frame, data frame extension (e.g., a tibble), or a lazy data frame (e.g., from dbplyr or dtplyr).
.nest_data	A list-column containing data frames
...	Variables to group by.
wt	Frequency weights. Can be NULL or a variable: If NULL (the default), counts the number of rows in each group. If a variable, computes sum(wt) for each group.
sort	If TRUE, will show the largest groups at the top.
name	The name of the new column in the output.

Details

nest_count() and nest_add_count() are largely wrappers for dplyr::count() and dplyr::add_count() and maintain the functionality of count() and add_count() within each nested data frame. For more information on count() and add_count(), please refer to the documentation in dplyr.

Value

An object of the same type as .data. Each object in the column .nest_data will also be of the same type as the input. nest_count() and nest_add_count() group each object in .nest_data transiently, so the output returned in .nest_data will have the same groups as the input.

Examples

gm_nest <- gapminder::gapminder %>% tidyr::nest(country_data = -continent)

# count the number of times each country appears in each nested tibble
gm_nest %>% nest_count(country_data, country)
gm_nest %>% nest_add_count(country_data, country)

# count the sum of population for each country in each nested tibble
gm_nest %>% nest_count(country_data, country, wt = pop)
gm_nest %>% nest_add_count(country_data, country, wt = pop)

nplyr documentation built on June 8, 2025, 10:44 a.m.