summarise.dtplyr_step {dtplyr}

Summarise each group to one row

Description

This is a method for the dplyr summarise() generic. It is translated to the j argument of ⁠[.data.table⁠.

Usage

## S3 method for class 'dtplyr_step'
summarise(.data, ..., .by = NULL, .groups = NULL)

Arguments

.data

A lazy_dt().

...

<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. min(x), n(), or sum(is.na(y)).

• 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.

.by

<tidy-select> Optionally, a selection of columns to group by for just this operation, functioning as an alternative to group_by(). For details and examples, see ?dplyr_by.

.groups

Grouping structure of the result.

• "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 .data.

• "rowwise": Each row is its own group.

When .groups is 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.

Examples

library(dplyr, warn.conflicts = FALSE)

dt <- lazy_dt(mtcars)

dt %>%
  group_by(cyl) %>%
  summarise(vs = mean(vs))

dt %>%
  group_by(cyl) %>%
  summarise(across(disp:wt, mean))