Apply a function to each group

These are methods for the dplyr group_map() and group_modify() generics. They are both translated to [.data.table.

Usage

# S3 method for class 'dtplyr_step'
group_modify(.data, .f, ..., keep = FALSE)

# S3 method for class 'dtplyr_step'
group_map(.data, .f, ..., keep = FALSE)

Arguments

.data

A lazy_dt()

.f

The name of a two argument function. The first argument is passed .SD,the data.table representing the current group; the second argument is passed .BY, a list giving the current values of the grouping variables. The function should return a list or data.table.

...

Additional arguments passed to .f

keep

Not supported for lazy_dt.

Value

group_map() applies .f to each group, returning a list. group_modify() replaces each group with the results of .f, returning a modified lazy_dt().

Examples

library(dplyr)

dt <- lazy_dt(mtcars)

dt %>%
  group_by(cyl) %>%
  group_modify(head, n = 2L)
#> Source: local data table [6 x 11]
#> Groups: cyl
#> Call:   `_DT16`[, head(.SD, .BY, n = ~2L), by = .(cyl)]
#> 
#>     cyl   mpg  disp    hp  drat    wt  qsec    vs    am  gear  carb
#>   <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl>
#> 1     6  21    160    110  3.9   2.62  16.5     0     1     4     4
#> 2     6  21    160    110  3.9   2.88  17.0     0     1     4     4
#> 3     4  22.8  108     93  3.85  2.32  18.6     1     1     4     1
#> 4     4  24.4  147.    62  3.69  3.19  20       1     0     4     2
#> 5     8  18.7  360    175  3.15  3.44  17.0     0     0     3     2
#> 6     8  14.3  360    245  3.21  3.57  15.8     0     0     3     4
#> 
#> # Use as.data.table()/as.data.frame()/as_tibble() to access results

dt %>%
  group_by(cyl) %>%
  group_map(head, n = 2L)
#> [[1]]
#>      mpg  disp    hp  drat    wt  qsec    vs    am  gear  carb
#>    <num> <num> <num> <num> <num> <num> <num> <num> <num> <num>
#> 1:    21   160   110   3.9 2.620 16.46     0     1     4     4
#> 2:    21   160   110   3.9 2.875 17.02     0     1     4     4
#> 
#> [[2]]
#>      mpg  disp    hp  drat    wt  qsec    vs    am  gear  carb
#>    <num> <num> <num> <num> <num> <num> <num> <num> <num> <num>
#> 1:  22.8 108.0    93  3.85  2.32 18.61     1     1     4     1
#> 2:  24.4 146.7    62  3.69  3.19 20.00     1     0     4     2
#> 
#> [[3]]
#>      mpg  disp    hp  drat    wt  qsec    vs    am  gear  carb
#>    <num> <num> <num> <num> <num> <num> <num> <num> <num> <num>
#> 1:  18.7   360   175  3.15  3.44 17.02     0     0     3     2
#> 2:  14.3   360   245  3.21  3.57 15.84     0     0     3     4
#>