How to assign multiple values with map()?

[matt_loop]

Hello,

Please could you help with (what I thought was going to be) a simple map function? I wish to assign values by mapping through a list. I can do this OK for a single value using the purrr::assign_in() function, as shown in the reprex. I wish to assign a vector of values (for example a sequence of c(99, 100, 101) in place of existing values, but I cannot work it out.

I spent hours on this last night without a breakthrough, so any advice would be welcome.

library(tidyverse)
library(lubridate)
#> 
#> Attaching package: 'lubridate'
#> The following objects are masked from 'package:base':
#> 
#>     date, intersect, setdiff, union

oranges <- list(
  tibble(
    admit_date = seq.Date(from = as_date("2020-02-01"), by = "day", length.out = 12),
    vals = seq(1:12)
  ),
  tibble(
    admit_date = seq.Date(from = as_date("2020-02-08"), by = "day", length.out = 12),
    vals = seq(13, 24)
  ))


# To assign a single value (99)
map(oranges, ~assign_in(.x, c(2,1), 99))
#> [[1]]
#> # A tibble: 12 x 2
#>    admit_date  vals
#>    <date>     <dbl>
#>  1 2020-02-01    99
#>  2 2020-02-02     2
#>  3 2020-02-03     3
#>  4 2020-02-04     4
#>  5 2020-02-05     5
#>  6 2020-02-06     6
#>  7 2020-02-07     7
#>  8 2020-02-08     8
#>  9 2020-02-09     9
#> 10 2020-02-10    10
#> 11 2020-02-11    11
#> 12 2020-02-12    12
#> 
#> [[2]]
#> # A tibble: 12 x 2
#>    admit_date  vals
#>    <date>     <dbl>
#>  1 2020-02-08    99
#>  2 2020-02-09    14
#>  3 2020-02-10    15
#>  4 2020-02-11    16
#>  5 2020-02-12    17
#>  6 2020-02-13    18
#>  7 2020-02-14    19
#>  8 2020-02-15    20
#>  9 2020-02-16    21
#> 10 2020-02-17    22
#> 11 2020-02-18    23
#> 12 2020-02-19    24

# Attempt to map several values with assignment operator
map(oranges, ~.x[10:12,2] <- c(99, 100, 101))
#> Error in ~.x[10:12, 2] <- c(99, 100, 101): object '.x' not found

^{Created on 2023-02-26 by the reprex package (v0.3.0)}

p.s. I'm on purrr version 0.3.4 as I've not been able to compile version 1.0.1.

[nirgrahamuk]

map(oranges, \(x) {
      x[["vals"]][10:12] <- 99:101
      x
    })

[matt_loop]

Hi,
Thanks. It looks like your thinking is to create a "local" function (if that is the terminology). What is the backslash use here?
I'm sorry to say the code didn't work for me, I got:
Error: unexpected input in "map(oranges, \"

Looks like we're on the right track though.

[nirgrahamuk]

Its the modern syntax for anonymous functions in R; it can be replaced with the old function keyword if you are using an old version of R

[mara]

A bit more info on @nirgrahamuk's explanation (which is 100% correct) re. the change in R 4.1.0 which introduced the use of \ for anonymous functions can be found in this write up:

New features in R 4.1.0

(The relevant section is entitled "Shorthand syntax for anonymous functions")

[matt_loop]

Ah, I see!
Yes, time to update, as I'm using v 4.0.3
Many thanks @nirgrahamuk for solving this one.