Formatting ggplot2 axis labels with commas (and K? MM?) if I already have a y-scale

Question

I am trying to format Cost and Revenue (both in thousands) and Impressions (in millions) data for a ggplot graph's y-axis labels.

My plot runs from 31 days ago to 'yesterday' and uses the min and max values over that period for the ylim(c(min,max)) option. Showing just the Cost example,

library(ggplot2) library(TTR)  set.seed(1984)  #make series start <- as.Date('2016-01-01') end <- Sys.Date()  days <- as.numeric(end - start)  #make cost and moving averages cost <- rnorm(days, mean = 45400, sd = 11640) date <- seq.Date(from = start, to = end - 1, by = 'day')  cost_7 <- SMA(cost, 7) cost_30 <- SMA(cost, 30)  df <- data.frame(Date = date, Cost = cost, Cost_7 = cost_7, Cost_30 = cost_30)   # set parameters for window left <- end - 31 right <- end - 1  # plot series ggplot(df, aes(x = Date, y = Cost))+ geom_line(lwd = 0.5) + geom_line(aes(y = Cost_7), col = 'red', linetype = 3, lwd = 1) + geom_line(aes(y = Cost_30), col = 'blue', linetype = 5, lwd = 0.75) + xlim(c(left, right)) +  ylim(c(min(df$Cost[df$Date > left]), max(df$Cost[df$Date > left]))) + xlab("") 

I would a) like to represent thousands and millions on the y-axis with commas, and b) like those numbers abbreviated and with 'K' for thousands or 'MM' for millions. I realize b) may be a tall order, but for now a) cannot be accomplished with

ggplot(...) + ... + ylim(c(min, max)) + scale_y_continuous(labels = comma)

Because the following error is thrown:

## Scale for 'y' is already present. Adding another scale for 'y', which ## will replace the existing scale. 

I have tried putting the scale_y_continuous(labels = comma) section after the geom_line()layer (which throws the error above) or at the end of all the ggplot layers, which overrides my limits in the ylim call and then throws the error above, anyway.

Any ideas?

Answer 1

For the comma formatting, you need to include the scales library for label=comma. The "error" you discussed is actually just a warning, because you used both ylim and then scale_y_continuous. The second call overrides the first. You can instead set the limits and specify comma-separated labels in a single call to scale_y_continuous:

library(scales)  ggplot(df, aes(x = Date, y = Cost))+   geom_line(lwd = 0.5) +   geom_line(aes(y = Cost_7), col = 'red', linetype = 3, lwd = 1) +   geom_line(aes(y = Cost_30), col = 'blue', linetype = 5, lwd = 0.75) +   xlim(c(left, right)) +    xlab("") +   scale_y_continuous(label=comma, limits=c(min(df$Cost[df$Date > left]),                                             max(df$Cost[df$Date > left]))) 

Another option would be to melt your data to long format before plotting, which reduces the amount of code needed and streamlines aesthetic mappings:

library(reshape2)  ggplot(melt(df, id.var="Date"),         aes(x = Date, y = value, color=variable, linetype=variable))+   geom_line() +   xlim(c(left, right)) +    labs(x="", y="Cost") +   scale_y_continuous(label=comma, limits=c(min(df$Cost[df$Date > left]),                                             max(df$Cost[df$Date > left]))) 

Either way, to put the y values in terms of thousands or millions you could divide the y values by 1,000 or 1,000,000. I've used dollar_format() below, but I think you'll also need to divide by the appropriate power of ten if you use unit_format (per @joran's suggestion). For example:

div=1000  ggplot(melt(df, id.var="Date"),         aes(x = Date, y = value/div, color=variable, linetype=variable))+   geom_line() +   xlim(c(left, right)) +    labs(x="", y="Cost (Thousands)") +   scale_y_continuous(label=dollar_format(),                      limits=c(min(df$Cost[df$Date > left]),                                max(df$Cost[df$Date > left]))/div) 

Use scale_color_manual and scale_linetype_manual to set custom colors and linetypes, if desired.