CODEWITHSUNDEEP
rlazy-evaluationtidyversepurrrrlang
Christopher Peralta
Christopher Peralta

Reputation: 431

How can I use purrr:: invoke_map(), on a function that uses enquo()?

Sorry, I know the title isn't the best.

So, I'm trying to write a function that checks whether the output of 2 functions is the same. I'm trying to do this with purrr::invoke_map(). However, I'm struggling to get it to work with any function that uses enquo().

I assume the issue is because the arguments are being evaluated before I want them to be evaluated. 

library(tidyverse)

check_output <- function(function_list, param_list = NULL){
  param_list <- list(param_list) 
  output <- invoke_map(.f = function_list, .x = param_list) 
  identical(output[1], output[2])
}

check_output(function_list = list(cumprod, cumsum),  # This works
             param_list = list(x = iris$Sepal.Length))

check_output(function_list = list(cumsum, cumsum), # This works
             param_list = list(x = iris$Sepal.Length))

m <- function(data, col_name){ # Enquo test function
  col_name <- enquo(col_name)
 data %>% 
    select(!!col_name)
}
n <- m

n(iris, Species) # Seeing if the functions work

check_output(function_list = list(m, n),     # The call doesn't work
             param_list = list(data = iris, col_name = Species))

Upvotes: 1

Views: 473

Answers (1)

Christopher Peralta
Christopher Peralta

Reputation: 431

I solved my problem by adding a helper function called add_quo, which turns the appropriate arguments into quosures. 

require(purrr)
require(magrittr) 
require(rlang) # add_quo uses this package

add_quo <- function(...) {
  ## Formats arguments for use in invoke_map()

  # Create a logical vector for use as an index below
  index <- exprs(...) %>%                       # Captures the arguments
    unlist() %>%                                # Makes them mappable
    map_if(negate(is.name), 
           .f = function(x) {return(TRUE)}) %>% # Replaces unnecessary args with TRUE
    map_if(is.name, as_character) %>%           # Converts named arguments to characters
    map_if(is.character, exists) %>%            # Replaces named args that aren't objects as FALSE
    unlist()                                    # To make index mappable

  # Wraps named args that aren't objects in new_quosure()
  exprs(...) %>%                    # Captures arguments
    unlist() %>%                    # Makes them mappable
    map_if(!index, new_quosure,     # Wraps non-object named arg in new_quosure()
           env = global_env()) %>%  # new_quosure() used instead of quo() as env must be global
    map_if(index, eval) %>%         # Removes expr() formatting
    list()                          # Makes arguments usable in invoke_map()
}

is.output.same<- function(.f_list, ...) {
  ## Checks to see if functions produce identical output

  param_list <- add_quo(...) # Enables function with dplyr syntax to work
  invoke_map(.f = .f_list, .x = param_list) %>%  # Pass args to functions
    reduce(identical) # Sees if all outputs are identical
}

check_output(function_list = list(m, n), data = iris, col_name = Species) #now works

Upvotes: 1

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