CODEWITHSUNDEEP
rggplot2logarithm
panuffel
panuffel

Reputation: 684

In ggplot, how do you log scale with positive as well as negative values?

I have data that have exponential behavior in positive and negative direction. How can I log-scale them in ggplot?

Example:

dat <- data.frame(x=sample(c(exp(runif(100,0,10)),-exp(runif(100,0,10)))))
ggplot(dat, aes(seq_along(x),x)) + 
    geom_point()

Not working

dat <- data.frame(x=sample(c(exp(runif(100,0,10)),-exp(runif(100,0,10)))))
ggplot(dat, aes(seq_along(x),x)) + 
    geom_point() +
scale_y_continuous(trans='log')

Thanks :)

Upvotes: 2

Views: 1065

Answers (1)

Tim
Tim

Reputation: 737

The log transformation is not defined for negative values, which is why it does not work. An alternative would be to use a pseudo-log transformation, which is defined for all real numbers:

    dat <- data.frame(x=sample(c(exp(runif(100, 0, 10)), -exp(runif(100, 0, 10)))))
    ggplot(dat, aes(seq_along(x), x)) + 
      geom_point() +
      scale_y_continuous(trans='pseudo_log')

Do note that for values close to zero the pseudo-log transformation approaches a linear transformation instead of a log transformation. This means a value like 0.2 will be plotted close to 0.2, instead of close to log(0.2), which equals to about -1.6.

Upvotes: 3

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