Summarise each group down to one rowSource:
summarise() creates a new data frame. It returns one row for each
combination of grouping variables; if there are no grouping variables, the
output will have a single row summarising all observations in the input. It
will contain one column for each grouping variable and one column for each of
the summary statistics that you have specified.
summarize() are synonyms.
summarise(.data, ..., .by = NULL, .groups = NULL) summarize(.data, ..., .by = NULL, .groups = NULL)
A data frame, data frame extension (e.g. a tibble), or a lazy data frame (e.g. from dbplyr or dtplyr). See Methods, below, for more details.
data-masking> Name-value pairs of summary functions. The name will be the name of the variable in the result.
The value can be:
A vector of length 1, e.g.
A data frame, to add multiple columns from a single expression.
Returning values with size 0 or >1 was deprecated as of 1.1.0. Please use
reframe()for this instead.
"drop_last": dropping the last level of grouping. This was the only supported option before version 1.0.0.
"drop": All levels of grouping are dropped.
"keep": Same grouping structure as
"rowwise": Each row is its own group.
.groupsis not specified, it is chosen based on the number of rows of the results:
If all the results have 1 row, you get "drop_last".
If the number of rows varies, you get "keep" (note that returning a variable number of rows was deprecated in favor of
reframe(), which also unconditionally drops all levels of grouping).
In addition, a message informs you of that choice, unless the result is ungrouped, the option "dplyr.summarise.inform" is set to
FALSE, or when
summarise()is called from a function in a package.
An object usually of the same type as
The rows come from the underlying
The columns are a combination of the grouping keys and the summary expressions that you provide.
Data frame attributes are not preserved, because
summarise()fundamentally creates a new data frame.
The data frame backend supports creating a variable and using it in the
same summary. This means that previously created summary variables can be
further transformed or combined within the summary, as in
However, it also means that summary variables with the same names as previous
variables overwrite them, making those variables unavailable to later summary
This behaviour may not be supported in other backends. To avoid unexpected results, consider using new names for your summary variables, especially when creating multiple summaries.
This function is a generic, which means that packages can provide implementations (methods) for other classes. See the documentation of individual methods for extra arguments and differences in behaviour.
The following methods are currently available in loaded packages:
tbl_lazy), dplyr (
# A summary applied to ungrouped tbl returns a single row mtcars %>% summarise(mean = mean(disp), n = n()) #> mean n #> 1 230.7219 32 # Usually, you'll want to group first mtcars %>% group_by(cyl) %>% summarise(mean = mean(disp), n = n()) #> # A tibble: 3 × 3 #> cyl mean n #> <dbl> <dbl> <int> #> 1 4 105. 11 #> 2 6 183. 7 #> 3 8 353. 14 # Each summary call removes one grouping level (since that group # is now just a single row) mtcars %>% group_by(cyl, vs) %>% summarise(cyl_n = n()) %>% group_vars() #> `summarise()` has grouped output by 'cyl'. You can override using the #> `.groups` argument. #>  "cyl" # BEWARE: reusing variables may lead to unexpected results mtcars %>% group_by(cyl) %>% summarise(disp = mean(disp), sd = sd(disp)) #> # A tibble: 3 × 3 #> cyl disp sd #> <dbl> <dbl> <dbl> #> 1 4 105. NA #> 2 6 183. NA #> 3 8 353. NA # Refer to column names stored as strings with the `.data` pronoun: var <- "mass" summarise(starwars, avg = mean(.data[[var]], na.rm = TRUE)) #> # A tibble: 1 × 1 #> avg #> <dbl> #> 1 97.3 # Learn more in ?dplyr_data_masking # In dplyr 1.1.0, returning multiple rows per group was deprecated in favor # of `reframe()`, which never messages and always returns an ungrouped # result: mtcars %>% group_by(cyl) %>% summarise(qs = quantile(disp, c(0.25, 0.75)), prob = c(0.25, 0.75)) #> Warning: Returning more (or less) than 1 row per `summarise()` group was #> deprecated in dplyr 1.1.0. #> ℹ Please use `reframe()` instead. #> ℹ When switching from `summarise()` to `reframe()`, remember that #> `reframe()` always returns an ungrouped data frame and adjust #> accordingly. #> `summarise()` has grouped output by 'cyl'. You can override using the #> `.groups` argument. #> # A tibble: 6 × 3 #> # Groups: cyl  #> cyl qs prob #> <dbl> <dbl> <dbl> #> 1 4 78.8 0.25 #> 2 4 121. 0.75 #> 3 6 160 0.25 #> 4 6 196. 0.75 #> 5 8 302. 0.25 #> 6 8 390 0.75 # -> mtcars %>% group_by(cyl) %>% reframe(qs = quantile(disp, c(0.25, 0.75)), prob = c(0.25, 0.75)) #> # A tibble: 6 × 3 #> cyl qs prob #> <dbl> <dbl> <dbl> #> 1 4 78.8 0.25 #> 2 4 121. 0.75 #> 3 6 160 0.25 #> 4 6 196. 0.75 #> 5 8 302. 0.25 #> 6 8 390 0.75