Change colours to defined palette for ggplot objects

Question

I would like to change the default colours to a specific palette for all geom_* type objects by using a function.

Below is an example for geom_lin

Answer 1

The following should do what you're after. Note that it only changes colours that are mapped to variables. Colour passed directly to the geom_* won't be affected (there's an example below). For an approach that modifies colour or fill (whichever is mapped first), see the bottom half of this post.

change_colours <- function(p, palette) {
  n <- nlevels(p$data[[deparse(p$mapping$group)]])
  tryCatch(as.character(palette), 
           error=function(e) stop('palette should be a vector of colours', call.=FALSE))
  if(n > length(palette)) stop('Not enough colours in palette.')
  pal <- function(n) palette[seq_len(n)]
  p + theme_light() + discrete_scale('colour', 'foo', pal)
}

# Here, df is from the OP's post
p <- ggplot(df, aes(x=TS, y=price, group=stock)) 

Examples:

# NB: custom_pal is defined in the OP's post
change_colours(p + geom_line(aes(colour=stock)), custom_pal)

change_colours(p + geom_point(aes(colour=stock)), custom_pal)

And with a different palette:

change_colours(p + geom_smooth(aes(colour=stock)), 
               c('firebrick', 'midnightblue', 'violet', 'seagreen'))

As mentioned above, this will only change colour and fill that are mapped to variables. For example, it'll have no effect on the colours for the following:

change_colours(p + geom_point(colour=rep(c('tomato', 'hotpink', 'cadetblue'), each=300)), 
               custom_pal)

---

In response to the OP's comment, you can easily detect what types of mappings are being used (e.g. alpha, colour, fill). Just look at p$layers[[1]]$mapping.

If we assume that the first fill or colour mapping of the first layer is the mapping for which you want to change colours, you can do:

change_colours <- function(p, palette, type) {
  n <- nlevels(p$data[[deparse(p$mapping$group)]])
  tryCatch(as.character(palette), 
           error=function(e) stop('palette should be a vector of colours', call.=FALSE))
  if(n > length(palette)) stop('Not enough colours in palette.')
  if(missing(type)) 
    type <- grep('colour|fill', names(p$layers[[1]]$mapping), value=TRUE)[1]
  pal <- function(n) palette[seq_len(n)]
  p + theme_light() + discrete_scale(type, 'foo', pal)
}

# Here, df is from the OP's post
p <- ggplot(df, aes(x=TS, y=price, group=stock))

Examples:

Changing fill instead of colour:

change_colours(p + geom_point(aes(fill=stock), pch=21), 
               c('white', 'grey50', 'grey80'))

Showing priority of first mapped colour/fill aesthetic:

change_colours(p + geom_point(aes(fill=stock, color=stock), pch=21) +
                 geom_smooth(aes(color=stock)), 
               c('black', 'grey50', 'grey80'))

change_colours(p + geom_point(aes(color=stock, fill=stock), pch=21) +
                 geom_smooth(aes(color=stock)), 
               c('black', 'grey50', 'grey80'))

Override the priority of the first mapped aesthetic with the type argument, e.g.:

change_colours(p + geom_point(aes(color=stock, fill=stock), pch=21) +
                 geom_smooth(aes(color=stock)), 
               c('black', 'grey50', 'grey80'), type='fill')