Named vector "by" arguments for `dplyr::_join` functions [duplicate] - r

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How to join (merge) data frames (inner, outer, left, right)
(13 answers)
Closed 2 years ago.
I am writing a function to dplyr::_join two dataframes by different columns, with the column name of the first dataframe dynamically specified as a function argument. I believe I need to use rlang quasiquotation/metaprogramming but haven't been able to get a working solution. I appreciate any suggestions!
library(dplyr)
library(rlang)
library(palmerpenguins)
# Create a smaller dataset
penguins <-
penguins %>%
group_by(species) %>%
slice_head(n = 4) %>%
ungroup()
# Create a colors dataset
penguin_colors <-
tibble(
type = c("Adelie", "Chinstrap", "Gentoo"),
color = c("orange", "purple", "green")
)
# Without function --------------------------------------------------------
# Join works with character vectors
left_join(
penguins, penguin_colors, by = c("species" = "type")
)
#> # A tibble: 12 x 9
#> species island bill_length_mm bill_depth_mm flipper_length_… body_mass_g
#> <chr> <fct> <dbl> <dbl> <int> <int>
#> 1 Adelie Torge… 39.1 18.7 181 3750
#> 2 Adelie Torge… 39.5 17.4 186 3800
#> 3 Adelie Torge… 40.3 18 195 3250
#> 4 Adelie Torge… NA NA NA NA
#> 5 Chinst… Dream 46.5 17.9 192 3500
#> 6 Chinst… Dream 50 19.5 196 3900
#> 7 Chinst… Dream 51.3 19.2 193 3650
#> 8 Chinst… Dream 45.4 18.7 188 3525
#> 9 Gentoo Biscoe 46.1 13.2 211 4500
#> 10 Gentoo Biscoe 50 16.3 230 5700
#> 11 Gentoo Biscoe 48.7 14.1 210 4450
#> 12 Gentoo Biscoe 50 15.2 218 5700
#> # … with 3 more variables: sex <fct>, year <int>, color <chr>
# Join works with data-variable and character vector
left_join(
penguins, penguin_colors, by = c(species = "type")
)
#> # A tibble: 12 x 9
#> species island bill_length_mm bill_depth_mm flipper_length_… body_mass_g
#> <chr> <fct> <dbl> <dbl> <int> <int>
#> 1 Adelie Torge… 39.1 18.7 181 3750
#> 2 Adelie Torge… 39.5 17.4 186 3800
#> 3 Adelie Torge… 40.3 18 195 3250
#> 4 Adelie Torge… NA NA NA NA
#> 5 Chinst… Dream 46.5 17.9 192 3500
#> 6 Chinst… Dream 50 19.5 196 3900
#> 7 Chinst… Dream 51.3 19.2 193 3650
#> 8 Chinst… Dream 45.4 18.7 188 3525
#> 9 Gentoo Biscoe 46.1 13.2 211 4500
#> 10 Gentoo Biscoe 50 16.3 230 5700
#> 11 Gentoo Biscoe 48.7 14.1 210 4450
#> 12 Gentoo Biscoe 50 15.2 218 5700
#> # … with 3 more variables: sex <fct>, year <int>, color <chr>
# Join does NOT work with character vector and data-variable
left_join(
penguins, penguin_colors, by = c(species = type)
)
#> Error in standardise_join_by(by, x_names = x_names, y_names = y_names): object 'type' not found
# With function -----------------------------------------------------------
# Version 1: Without tunneling
add_colors <- function(data, var) {
left_join(
data, penguin_colors, by = c(var = "type")
)
}
add_colors(penguins, species)
#> Error: Join columns must be present in data.
#> x Problem with `var`.
add_colors(penguins, "species")
#> Error: Join columns must be present in data.
#> x Problem with `var`.
# Version 2: With tunneling
add_colors <- function(data, var) {
left_join(
data, penguin_colors, by = c("{{var}}" = "type")
)
}
add_colors(penguins, species)
#> Error: Join columns must be present in data.
#> x Problem with `{{var}}`.
add_colors(penguins, "species")
#> Error: Join columns must be present in data.
#> x Problem with `{{var}}`.
# Version 2: With tunneling and glue syntax
add_colors <- function(data, var) {
left_join(
data, penguin_colors, by = c("{{var}}" := "type")
)
}
add_colors(penguins, species)
#> Error: `:=` can only be used within a quasiquoted argument
add_colors(penguins, "species")
#> Error: `:=` can only be used within a quasiquoted argument
Created on 2020-10-05 by the reprex package (v0.3.0)
Here are related resources I consulted:
using `rlang` quasiquotation with `dplyr::_join` functions
https://dplyr.tidyverse.org/reference/join.html
https://speakerdeck.com/lionelhenry/interactivity-and-programming-in-the-tidyverse
https://dplyr.tidyverse.org/articles/programming.html
Thank you for your advice.

Answer 1

library(dplyr)
left_join(
penguins, penguin_colors, by = c(species = "type")
)
The reason why above works is because in by we are creating a named vector like this :
c(species = "type")
#species
# "type"
You can also do that via setNames :
setNames('type', 'species')
but notice that passing species without quotes fail.
setNames('type', species)
Error in setNames("type", species) : object 'species' not found
So create a named vector with setNames and pass character value in the function.
add_colors <- function(data, var) {
left_join(
data, penguin_colors, by = setNames('type', var)
)
}
add_colors(penguins, 'species')

Answer 2

To add to Ronak's solution you can also achieve this without quotes using ensym
Example:
add_colors <- function(data, var) {
left_join(
data, penguin_colors, by = set_names("type", nm = ensym(var))
)
}