Summarise each group to one row

This is a method for the dplyr dplyr::summarise() generic. It generates the SELECT clause of the SQL query, and generally needs to be combined with group_by().

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

Arguments

.data

A lazy data frame backed by a database query.

...

<data-masking> Variables, or functions of variables. Use desc() to sort a variable in descending order.

.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.

When .groups is not specified, it defaults to "drop_last".

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.

Value

Another tbl_lazy. Use dplyr::show_query() to see the generated query, and use collect() to execute the query and return data to R.

Examples

library(dplyr, warn.conflicts = FALSE)

db <- memdb_frame(g = c(1, 1, 1, 2, 2), x = c(4, 3, 6, 9, 2))
db %>%
  summarise(n()) %>%
  show_query()
#> <SQL>
#> SELECT COUNT(*) AS `n()`
#> FROM `dbplyr_N9PgDPOtnO`

db %>%
  group_by(g) %>%
  summarise(n()) %>%
  show_query()
#> <SQL>
#> SELECT `g`, COUNT(*) AS `n()`
#> FROM `dbplyr_N9PgDPOtnO`
#> GROUP BY `g`