How to accurately display SI prefix for numbers in y-axis scale of plot made with ggplot2 in R?

Question

I have the following plot, generated using this code

plt <- ggplot(d2, aes_string(x=names(same_df)[1],y= "value")) + 
    geom_point(aes(color = variable), size = 1)+ theme_bw()+
    theme(legend.text=element_text(size=14), legend.title=element_text(size=14))+
    theme(axis.text=element_text(size=20)) +
    theme(axis.title=element_text(size=20,face="bold")) + scale_color_discrete(name = "title", labels = c("1", "2", "3", "4","5","6","7","8","9")) + labs(x = "x", y = "y")+ guides(colour = guide_legend(override.aes = list(size=4),ncol=2,title.hjust=0.5))+theme(plot.margin=unit(c(0,0,0,0),"mm"))

However I need SI prefix notation for the numbers in the y-axis, to get that I did the following steps,

library("sos")

To use the findFn in sitools package

findFn("{SI prefix}") 

Then I use the f2si in the labels to convert a floating point number number to number with a SI prefix

plt2 <- plt + scale_y_continuous(labels=f2si)

The resulting plot looks like this,

While the f2si accurately changed the y axis for -1e^-0.8 to -10 n, it does not accurately display the value for 0 and 1e^-0.8 which would be 0 and 10 n respectively. Could someone please suggest what should be corrected here so that the numbers are displayed as they should be throughout.

Thanks.

Syndicalism

See here. – Cabezon

Answer 1

I was not able to reproduce your behaviour. See this:

df <- data.frame(x=runif(100), y=(runif(100)-1/2)/1e8)
p <- ggplot(df, aes(x, y)) + geom_point()
p + scale_y_continuous(labels=f2si)

I have also found another similar function, if you don't like "0 n" label:

  format_si <- function(...) {
  # Based on code by Ben Tupper
  # https://stat.ethz.ch/pipermail/r-help/2012-January/299804.html

  function(x) {
    limits <- c(1e-24, 1e-21, 1e-18, 1e-15, 1e-12,
                1e-9,  1e-6,  1e-3,  1e0,   1e3,
                1e6,   1e9,   1e12,  1e15,  1e18,
                1e21,  1e24)
    prefix <- c("y",   "z",   "a",   "f",   "p",
                "n",   "µ",   "m",   " ",   "k",
                "M",   "G",   "T",   "P",   "E",
                "Z",   "Y")

    # Vector with array indices according to position in intervals
    i <- findInterval(abs(x), limits)

    # Set prefix to " " for very small values < 1e-24
    i <- ifelse(i==0, which(limits == 1e0), i)

    paste(format(round(x/limits[i], 1),
                 trim=TRUE, scientific=FALSE, ...),
          prefix[i])
  }
}

p + scale_y_continuous(labels=format_si())

Gomes

Thanks for your suggestion, It works now, I guess you mean p + scale_y_continuous(labels=format_si()) in the last line of the code to remove n near 0. – Syndicalism

I really like the format_si() function you've written since it's easy to customize, like replacing "B" for "G" to represent billions, if so desired. – Wivern

@Wivern Thanks, my pleasure. – Gomes