scale_color_gradientn errors when using labels

[tvatter]

---

I found a problem with scale_color_gradientn.

I expected to be able to use the labels argument to tweak the labels, but I must be doing something wrong.

Here is the code to reproduce what I believe to be a bug:

library(tidyverse)
library(scales)
#> 
#> Attaching package: 'scales'
#> The following object is masked from 'package:purrr':
#> 
#>     discard
#> The following object is masked from 'package:readr':
#> 
#>     col_factor

set.seed(1)
nyears = 20
df <- tibble( # a toy dataset
  year_idx = rep(1:nyears, each = 12),
  month = rep(1:12, nyears),
  passengers = rnorm(nyears * 12, mean = 10 * rep(1:nyears, each = 12))
)

years <- 1970:(1970 + nyears - 1)

ggplot(df, aes(x = month, y = passengers, color = year_idx, group = year_idx)) +
  geom_line() # works

ggplot(df, aes(x = month, y = passengers, color = year_idx, group = year_idx)) +
  geom_line() +
  scale_color_gradientn(colours = (scales::hue_pal())(9),
                        labels = function(idx) years[idx]) # errors
#> Error in `scale_color_gradientn()`:
#> ! `breaks` and `labels` have different lengths.

^{Created on 2024-03-06 with reprex v2.1.0}

[tvatter]

I forgot to mention, I'm running R 4.3.2 and I think that the same thing was working as expected in a previous R version

[teunbrand]

Automatic break calculation includes 0 as a break in your example, which cannot be used to index the years variable.
If you're setting the labels argument to anything other than a formatting function, it is advised to also set the breaks argument.
As this is neither a bug report nor feature request and the error is thrown correctly, I'll close this issue.

[tvatter]

@teunbrand Awesome, thanks a lot for the explanation!