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I need to modify the scale of the y-axis in a ggplot2 graphic : I want to express the y-axis in thousands and not in units. For example, the labels have to be 0 ; 1,000 ; 2,000 ; 3,000 instead of 0 ; 1000000 ; 2000000 ; 3000000.

Please, don't tell me to divide my data by 1000 !

My question is the same as ggplot2 axis transformation by constant factor. But the solution provided here modifies the lables parameter of the scale_y_continuous function, whereas I need this parameter to be set to comma. With this solution I get the following breaks : 0 ; 1000 ; 2000 ; 3000 ... Breaks are expressed in thousands and not in millions and this is a good point, but I loose the comma labels. I want to see 1,000 ; 2,000 ; 3,000 and not 1000 ; 2000 ; 3000...

So modifying the lables parameter of the scale_y_continuous function isn't useful. That's why I think I have to work with the trans parameter of the scale_y_continuous function instead of the labels parameter.

There are a lot of built-in transformation that match the trans parameter and solve similar problems in the scales package (look at log_trans for example). So I tried to build my own homothetic transformation, with the code below.

library(ggplot2)

var0 <- c(1:100)
var1 <- 1000000*rnorm(100)

homothetic_breaks<- function (n = 5, base = 1000) 
{
  function(x) {
    rng <- (range(x, na.rm = TRUE)/base)
    min <- floor(rng[1])
    max <- ceiling(rng[2])
    if (max == min) 
      return(base*min)
    by <- floor((max - min)/n) + 1
    base*seq(min, max, by = by)
  }
}

homothetic_trans <- function(base = 1000) {
  trans <- function(x) x/base
  inv <- function(x) x*base
  trans_new(paste0("diviseur_par_", format(base)), trans, inv,
            homothetic_breaks(base=base), domain = c(-Inf, Inf))
}

data <- data.frame(var0,var1)
p <- ggplot(data,aes(var0,var1))+geom_path()
p <- p + scale_y_continuous(trans=homothetic_trans,labels = comma) 
p

When I run this code I get the following message : "Error: Input to str_c should be atomic vectors", and the breaks of the y axis arethe same as the ones I get when I run the following code : 

library(ggplot2)

var1 <- 1000*rnorm(100)
var0 <- c(1:100)

data <- data.frame(var0,var1)

p <- ggplot(data,aes(var0,var1))+geom_path()
p
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Giuliano
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  • Try `scale_y_continuous(trans="homothetic",labels = comma)`. If that "does not work" please describe exactly what "doesn't work". Are you getting an error? Is anything plotting at all? Are you getting the wrong breaks? Describe what you expect to happen and what actually happens. "Does not work" is not a description of a problem. – MrFlick Jun 24 '14 at 17:52
  • Thanks for your advice, but when I run your code I get the following message : "Error in match.fun(f)() : could not find function "trans_new"". The plot appears, but the y axis is not modified. – Giuliano Jun 25 '14 at 08:18
  • Solution of @MrFlick works if you add `library(scales)`. Fuction `trans_new()` is in this package – Didzis Elferts Jun 25 '14 at 13:17
  • The solution of MrFlick doesn't work : I get the same result as the one obtained with `p <- p + scale_y_continuous(trans="homothetic",labels = comma)` the breaks are still expressed in units and not in thousands – Giuliano Jun 25 '14 at 21:06

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