SI prefixes in ggplot2 axis labels

Question

I often plot graphs in GNU R / ggplot for some measurements related to bytes. The builtin axis labels are either plain numbers or scientific notation, ie 1 Megabyte = 1e6. I

Answer 1

Update: Recent versions of the scales package include functionality to print readable labels.

In this case, label_bytes can be used:

library(ggplot2)
library(scales)

bytes <- 2^seq(0,20) + rnorm(21, 4, 2)

my_data <- data.frame(
    bytes=as.integer(bytes),
    time=bytes / (1e4 + rnorm(21, 100, 3)) + 8
)

ggplot(data=my_data, aes(x=bytes, y=time)) +
    geom_point() +
    geom_line() +
    scale_x_log10("Message Size [Byte]", labels=label_bytes()) +
    scale_y_continuous("Round-Trip-Time [us]")

Or, if you prefer to have IEC units (KiB = 2^10, MiB = 2 ^ 20, ...), specify labels=label_bytes(units = "auto_binary"). For the result, check out the second plot in the original answer below as the result is very similar.

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Original answer

For bytes there is gdata::humanReadable. humanReadable supports both SI prefixes (1000 Byte = 1 KB) as well as the binary prefixes defined by the IEC (1024 Byte = 1 KiB).

This function humanReadableLabs allows to customise the parameters and takes care of NA values:

humanReadableLabs <- function(...) {
    function(x) {
        sapply(x, function(val) {
            if (is.na(val)) {
                return("")
            } else {
                return(
                    humanReadable(val, ...)
                )
            }
        })
    }
}

Now it is straightforward to change the labels to use SI prefixes and "byte" as the unit:

library(ggplot2)
library(gdata)

bytes <- 2^seq(0,20) + rnorm(21, 4, 2)

my_data <- data.frame(
    bytes=as.integer(bytes),
    time=bytes / (1e4 + rnorm(21, 100, 3)) + 8
)

humanReadableLabs <- function(...) {...}

ggplot(data=my_data, aes(x=bytes, y=time)) +
    geom_point() +
    geom_line() +
    scale_x_log10("Message Size [Byte]", labels=humanReadableLabs(standard="SI")) +
    scale_y_continuous("Round-Trip-Time [us]")

IEC prefixes are plotted by omitting standard="SI". Note that the breaks would have to be specified as well to have well-legible values.

ggplot(data=my_data, aes(x=bytes, y=time)) +
    geom_point() +
    geom_line() +
    scale_x_log10("Message Size [Byte]", labels=humanReadableLabs()) +
    scale_y_continuous("Round-Trip-Time [us]")