pass a df column name in a variable when creating a ggplot plot inside custom function

Question

I'm elaborating a function that creates a custom ggplot plot. The problem is that when I invoke the function and pass a df column name (let's say 'AREA') of a column that I'd like to use as the value of another variable (let`s say var) I get an Error: Discrete value supplied to continuous scale. But when I use that custom function with the same value (character 'AREA', not the variable var = 'AREA') it works. Moreover, when I use the exact ggplot code and pass the column name as variable var it also works fine.

Reproducible example:

library(sf)
library(tidyverse)
library(viridis)
library(rvest)

nc <- read_sf(system.file("shape/nc.shp", package = "sf"))

### Custom function
p_plot <- function(data,var){
  ggplot(nc) +
    geom_sf(aes(fill = !!ensym(var))) +
    scale_fill_gradientn("Area",colors = viridis(10)
    ) +
    ggtitle("Area of counties in North Carolina") +
    theme_bw()
}

nc <- read_sf(system.file("shape/nc.shp", package = "sf"))
var <- j<- 'AREA'

### This one works
ggplot(nc) +
  geom_sf(aes(fill = !!ensym(var))) +
  scale_fill_gradientn("Area",colors = viridis(10)
  ) +
  ggtitle("Area of counties in North Carolina") +
  theme_bw()

### This one also works
p_plot(data, "AREA")

### This one doesn't work:
### Error: Discrete value supplied to continuous scale
p_plot(data, j)

akrun akrun · Accepted Answer · 2020-01-17T19:45:57

0

votes

We can evaluate the j

p_plot(data, !!j)

pass a df column name in a variable when creating a ggplot plot inside custom function

1 Answers