Indian Style thousand separator in ggplot2 chart axes

Question

Indian style thousand separators are used like this. First separator at 3 digits (thousands) but thereafter separator at every two digits.

1
10
100
1,000
10,000
1,00,000
10,00,000
1,00,00,000
10,00,00,000

I know that I can change/format axes in ggplot2 chart by using scale_y_continuous(labels = scales::comma)

But how can I change the thousand separator placeholder in r ggplot2 chart axes according to Indian formats as described above.

A sample example

library(tidyverse)
iris %>%
  mutate(Petal.Length= Petal.Length*100000) %>%
  ggplot(aes(x= Species, y = Petal.Length)) +
  geom_col() +
  scale_y_continuous(labels = scales::comma)

^{Created on 2021-06-28 by the reprex package (v2.0.0)}

Answer 1

You can define your own formatting function and supply this as the labels argument to scale_y_continuous(). Here is an example using the base prettyNum() function:

library(ggplot2)

indian_comma <- function(x) {
  
  # Format the number, first dividing by 10 to place the first comma at the 
  # right point
  out <- prettyNum(x %/% 10, big.interval = 2L, big.mark = ",", scientific = FALSE)
  out <- paste0(out, x %% 10)
  
  # Switch between formatted and un-formatted depending on the size of the
  # number
  ifelse(
    x < 1000, x, out
  )
  
}

iris %>%
  mutate(Petal.Length= Petal.Length*100000) %>%
  ggplot(aes(x= Species, y = Petal.Length)) +
  geom_col() +
  scale_y_continuous(labels = indian_comma)

EDIT

Here's an alternative implementation using regular expressions. On balance I think I prefer the first option for clarity, but this is quite elegant:

indian_comma <- function(x) {
  x <- prettyNum(x, scientific = FALSE)
  gsub("(?<!^)(?=(\\d{2})+\\d$)", ",", x, perl = TRUE)
}