How to get case_when in dplyr accept conditions from character

I am trying to use case_when in shiny application in order to build an app, showing the preview of some selection policy expressed as a set of rules.

In the app, user can input expressions in case_when syntax, e.g.:

cond = "Age > 40 ~ 1, TRUE ~ 0"

and they should be substituted in case_when.

I am looking at rlang and trying to figure out how to get an expression from a character vector, e.g.

tibble::tribble(~Age,23,26,32,50,51,52,25,49,34,54) %>% 
  mutate(result = case_when(!!!quos(syms(cond))))

but, apparently, fail to get it right

Solution

How about with parse_exprs?

library(dplyr)
library(rlang)
cond <- "Age > 40 ~ 1, TRUE ~ 0"
cond <- gsub(",",";",cond)
repdata %>% mutate(result = case_when(!!!rlang::parse_exprs(cond)))
## A tibble: 10 x 2
#     Age result
#   <dbl>  <dbl>
# 1    23      0
# 2    26      0
# 3    32      0
# 4    50      1
# 5    51      1
# 6    52      1
# 7    25      0
# 8    49      1
# 9    34      0
#10    54      1

This is required because parse_expr returns one expression, whereas case_when requires 2 or more expressions (separated by commas in code) to have 2 cases. Meanwhile, parse_exprs returns 2 or more expressions, but it splits expressions on ;.

Data

repdata <- tibble::tribble(~Age,23,26,32,50,51,52,25,49,34,54)