[SOLVED] How to pass a filter statement as a function parameter in dplyr using quosure

How to pass a filter statement as a function parameter in dplyr using quosure

Using the dplyr package in R, I want to pass a filter statement as a parameter in a function. I don't know how to evaluate the statement as code instead of a string. When I try the code below, I get an error message. I'm assuming I need a quosure or something, but I don't fully grasp that concept.

data("PlantGrowth")

myfunc <- function(df, filter_statement) {
  df %>%
    filter(!!filter_statement)
}

myfunc(PlantGrowth, "group %in% c('trt1', 'trt2')")

>  Error: Argument 2 filter condition does not evaluate to a logical vector 

# Want to do the same as this:
# PlantGrowth %>%
#   filter(group %in% c('trt1', 'trt2'))

Solution

You can use parse_expr from rlang

library(dplyr)

myfunc <- function(df, filter_statement) {
   df %>% filter(eval(rlang::parse_expr(filter_statement)))
}

identical(myfunc(PlantGrowth, "group %in% c('trt1', 'trt2')"), 
      PlantGrowth %>% filter(group %in% c('trt1', 'trt2')))

#[1] TRUE

The same can be done using infamous eval and parse.

myfunc <- function(df, filter_statement) {
   df %>% filter(eval(parse(text = filter_statement)))
}