purrrplus

Background

In my work, I often need to run a function in R many times (for example in running a simulation). If any of these runs throw an error, all progress is lost. The tidyverse package purrrr provides functionality like safely which helps but makes subsequent analysis tricky. As a remedy, I wrote the package purrrplus which allows for running a function safely with easy analysis of errors and results.

Example

library(purrrplus)
library(tidyverse) # most useful with the tidyverse

Imagine you have a function (which returns a named list or a named vector and might throw an error):

calculate_if_positive <- function(a, b){
  if(a < 0 & b < 0) {stop("Both numbers are negative.")}
  else if(a < 0) {stop("Just the first number is negative")}
  else if(b < 0) {stop("Just the second number is negative")}
  
  list(add = a + b,
       subtract = a - b,
       multiply = a * b,
       divide = a / b)
}

And you want to apply this function to each row of a data frame (which might contain irrelevant variables):

(numbers <- data_frame(a = c(-1, 0, 1, 2),
                      b = c(2, 1, 0, -1),
                      irrelevant = c("minneapolis", "st_paul", "minneapolis", "st_paul")))

## Warning: `data_frame()` was deprecated in tibble 1.1.0.
## Please use `tibble()` instead.

## # A tibble: 4 x 3
##       a     b irrelevant 
##   <dbl> <dbl> <chr>      
## 1    -1     2 minneapolis
## 2     0     1 st_paul    
## 3     1     0 minneapolis
## 4     2    -1 st_paul

pmap_safely adds an error and a result column (which come from applying the function) to the inputted data frame.

(output <- pmap_safely(numbers, calculate_if_positive))

## Note that the function does not use the following variables: irrelevant

## # A tibble: 4 x 5
##       a     b irrelevant  error                              result          
##   <dbl> <dbl> <chr>       <chr>                              <list>          
## 1    -1     2 minneapolis Just the first number is negative  <NULL>          
## 2     0     1 st_paul     <NA>                               <named list [4]>
## 3     1     0 minneapolis <NA>                               <named list [4]>
## 4     2    -1 st_paul     Just the second number is negative <NULL>

get_errors allows for quick analysis of errors:

get_errors(output)

## # A tibble: 10 x 5
##    variable   value       n_errors count error_rate
##    <chr>      <chr>          <int> <int>      <dbl>
##  1 a          -1                 1     1        1  
##  2 a          2                  1     1        1  
##  3 a          0                  0     1        0  
##  4 a          1                  0     1        0  
##  5 b          -1                 1     1        1  
##  6 b          2                  1     1        1  
##  7 b          0                  0     1        0  
##  8 b          1                  0     1        0  
##  9 irrelevant minneapolis        1     2        0.5
## 10 irrelevant st_paul            1     2        0.5

get_results filters out rows with errors and unnests results such that each item in the list that the function returns has its own column:

get_results(output)

## Removed 2 errors out of 4 rows.

## # A tibble: 2 x 7
##       a     b irrelevant  add_result subtract_result multiply_result
##   <dbl> <dbl> <chr>            <dbl>           <dbl>           <dbl>
## 1     0     1 st_paul              1              -1               0
## 2     1     0 minneapolis          1               1               0
## # … with 1 more variable: divide_result <dbl>