This is a method for the 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)
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.
<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.
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.
Another tbl_lazy
. Use show_query()
to see the generated
query, and use collect()
to execute the query
and return data to R.
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_pC2nZCgFGG`
db %>%
group_by(g) %>%
summarise(n()) %>%
show_query()
#> <SQL>
#> SELECT `g`, COUNT(*) AS `n()`
#> FROM `dbplyr_pC2nZCgFGG`
#> GROUP BY `g`