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

# S3 method for dtplyr_step
summarise(.data, ..., .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 vector of length n, e.g. quantile().

  • A data frame, to add multiple columns from a single expression.

.groups

[Experimental] 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.

Examples

library(dplyr, warn.conflicts = FALSE) dt <- lazy_dt(mtcars) dt %>% group_by(cyl) %>% summarise(vs = mean(vs))
#> Source: local data table [3 x 2] #> Call: `_DT36`[, .(vs = mean(vs)), keyby = .(cyl)] #> #> cyl vs #> <dbl> <dbl> #> 1 4 0.909 #> 2 6 0.571 #> 3 8 0 #> #> # Use as.data.table()/as.data.frame()/as_tibble() to access results
dt %>% group_by(cyl) %>% summarise(across(disp:wt, mean))
#> Source: local data table [3 x 5] #> Call: `_DT36`[, .(disp = mean(disp), hp = mean(hp), drat = mean(drat), #> wt = mean(wt)), keyby = .(cyl)] #> #> cyl disp hp drat wt #> <dbl> <dbl> <dbl> <dbl> <dbl> #> 1 4 105. 82.6 4.07 2.29 #> 2 6 183. 122. 3.59 3.12 #> 3 8 353. 209. 3.23 4.00 #> #> # Use as.data.table()/as.data.frame()/as_tibble() to access results