CODEWITHSUNDEEP
rlisttidyversepurrrtibble
Cettt
Cettt

Reputation: 11981

create a tibble where one column is a function

lets say I have a tibble which looks like this:

library(tidyverse)
tib <- tibble (a = 1:3, b = 4:6, d = -1:1)

I want to add a column to this tibble where each entry is a function with parameters a,b and d (like f(x) = ax^2 + bx +d). This would mean that (e.g) in the first row I would like to add the function f(x) = 1 x ^2 + 4 x -1, and so on.

I tried the following:

tib2 <- tib %>%
   mutate(fun = list(function(x) {a*x^2+b*x+d}))

This does not work since the functions do not know what a, b and d are.

I managed to build a work-around solution using the function mapply

lf <- mapply(function(a,b,d){return(function(x){a*x^2 + b*x + d})}, tib$a, tib$b, tib$d)
tib3 <- tib %>% 
  add_column(lf)

I was wondering if anyone knows a more elegant way of doing this within the tidyverse. It feels like there is a way using the map function from the purrr package, but I did not manage to get it working.

Thank you

Upvotes: 2

Views: 1088

Answers (1)

Paul
Paul

Reputation: 9107

When you used mutate in your example, you were giving it a list with one element (function). So this one function was recycled for all the other rows. Also, inside the definition of the function, it doesn't have any visibility of a, b or d.

You can instead use pmap so that each row has its own function.

tib2 <- tib %>%
  mutate(
    fun = pmap(
      list(a, b, d),
      ~function(x) ..1 * x^2 + ..2 * x + ..3))

tib2
#> # A tibble: 3 x 4
#>       a     b     d    fun
#>   <int> <int> <int> <list>
#> 1     1     4    -1  <fun>
#> 2     2     5     0  <fun>
#> 3     3     6     1  <fun>

tib2$fun[[1]](1)
#> [1] 4

Upvotes: 1

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