grouped case_when

gistfile1.txt

``` r
library(dplyr)
#> 
#> Attaching package: 'dplyr'
#> The following objects are masked from 'package:stats':
#> 
#>     filter, lag
#> The following objects are masked from 'package:base':
#> 
#>     intersect, setdiff, setequal, union
library(tibble)
tribble( ~a, ~b, ~c,
        "A",  1, "X",
        "A",  2, "X",
        "B",  1, "Y",
        "B",  2, "Y") %>%
  group_by(a) %>%
  summarise(case_when(
    c == "X" ~ sum(b),
    c == "Y" ~ sum(b) * -1,
    TRUE ~ NA_real_
  ))
#> `summarise()` regrouping output by 'a' (override with `.groups` argument)
#> # A tibble: 4 x 2
#> # Groups:   a [2]
#>   a     `case_when(c == "X" ~ sum(b), c == "Y" ~ sum(b) * -1, TRUE ~ NA_real_)`
#>   <chr>                                                                   <dbl>
#> 1 A                                                                           3
#> 2 A                                                                           3
#> 3 B                                                                          -3
#> 4 B                                                                          -3
```

<sup>Created on 2020-06-10 by the [reprex package](https://reprex.tidyverse.org) (v0.3.0)</sup>