summarise: Summarise multiple values to a single value.

Description

Summarise multiple values to a single value.

Usage

summarise(.data, ...)
summarise_(.data, ..., .dots)
summarize(.data, ...)
summarize_(.data, ..., .dots)

Arguments

.data

A tbl. All main verbs are S3 generics and provide methods for tbl_df, tbl_dt and tbl_sql.

...

Name-value pairs of summary functions like min(), mean(), max() etc.

.dots

Used to work around non-standard evaluation. See vignette("nse") for details.

Value

An object of the same class as .data. One grouping level will be dropped.

Data frame row names are silently dropped. To preserve, convert to an explicit variable.

Backend variations

Data frames are the only backend that supports creating a variable and using it in the same summary. See examples for more details.

Examples

Run this code

summarise(mtcars, mean(disp))
summarise(group_by(mtcars, cyl), mean(disp))
summarise(group_by(mtcars, cyl), m = mean(disp), sd = sd(disp))

# With data frames, you can create and immediately use summaries
by_cyl <- mtcars %>% group_by(cyl)
by_cyl %>% summarise(a = n(), b = a + 1)

## Not run: ------------------------------------
# # You can't with data tables or databases
# by_cyl_dt <- mtcars %>% tbl_dt() %>% group_by(cyl)
# by_cyl_dt %>% summarise(a = n(), b = a + 1)
# 
# by_cyl_db <- src_sqlite(":memory:", create = TRUE) %>%
#   copy_to(mtcars) %>% group_by(cyl)
# by_cyl_db %>% summarise(a = n(), b = a + 1)
## ---------------------------------------------

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