How to use query function of hashmap in mutate of dplyr pipe in R?-CodePudding

I would like to find a value using a hashmap and then use this value to calculate a new one. Usually I try to work efficiently, but I am not very proficient in R. I know the basics of dplyr pipes, so do no longer want to use for loops.

Here is a minimal reproducable example of the situation:

data("mtcars")

m.subset <- mtcars[2:7, 10:11]
letters <- c("a", "b", "c", "d", "e", "f")
m.subset <- cbind(m.subset, letters)

testmap <- hashmap()
testmap[c("a", "b", "c", "d", "e", "f")] <- c(4.0, 5.0, 6.0, 7.0, 8.0, 9.0)

m.subset %>% mutate(score1=query(testmap, letters)*gear) -> m.subset

Unfortunately, I get this error:

Error in `mutate()`:
! Problem while computing `score1 = query(testmap, letters) * gear`.
✖ `score1` must be size 6 or 1, not 0.
Run `rlang::last_error()` to see where the error occurred.

A note is that this works: score1=query(testmap, m.subset$letters[1])*m.subset$gear[1], where I can obviously interchange the 1 with an i and use a for loop. But I prefer not to, as a dplyr pipe is so nice to do columnwise calculations.

I also read several questions on StackOverflow, like error-in-r-mutate-must-be-size-4-or-1-not-0.

CodePudding user response：

Assuming you are using r2r for hashmap and query, you can try the following. Using map2 from purrr you can go through each element of letters and gear, and apply the function query using your testmap.

library(tidyverse)
library(r2r)

m.subset %>% 
  mutate(score1 = map2(
    letters,
    gear,
    ~ query(testmap, .x) * .y
  ))

Output

                  gear carb letters score1
Mazda RX4 Wag        4    4       a     16
Datsun 710           4    1       b     20
Hornet 4 Drive       3    1       c     18
Hornet Sportabout    3    2       d     21
Valiant              3    1       e     24
Duster 360           3    4       f     27