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I am trying to create a squared transform for the y-axis using scales::trans_new but am hitting an error.

MWE

data = data.frame(x = 1:10, y = runif(10), z=rnorm(10, 10)) library(ggplot2) ggplot(data, aes(x, y, size=z)) + geom_point() + scale_y_continuous(trans=scales::trans_new("sq", function(x) x^2, function(x) x^(1/2)))

gives the error

Error in if (zero_range(as.numeric(limits))) { :
missing value where TRUE/FALSE needed

I tries adding limits and domain but got the same error.

scale_y_continuous(trans=scales::trans_new("sq", function(x) x^2, function(x) x^(1/2)), limits=c(0,1)) scale_y_continuous(trans=scales::trans_new("sq", function(x) x^2, function(x) x^(1/2), domain=c(0,1)), limits=c(0,1))

It seesm to be the inverse argument that is causing the error - but all values of y are positive, so I don't understand. How can I do this please?

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  • why can't you just create a new variable for the y squared value and plot that? Commented Oct 29, 2018 at 20:10
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    @Mike ; because this takes care of axis scaling / lables -- it should be less effort ;) Commented Oct 29, 2018 at 20:13
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    last solution and then I will give up. scale_y_continuous(trans = scales::trans_new("sq", function(x){x^2}, function(x){sqrt(abs(x))})) Commented Oct 29, 2018 at 20:29
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    thanks @mike. Indeed adding abs worked. Dave2e has come to the same conclusion by the looks of it - but I thknk a slightly safer workaround. Thanks again for your help. Commented Oct 29, 2018 at 20:35

1 Answer 1

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It seems ggplot is using the inverse function to set the y-axis limits and axis labels. If y is near zero, gglot, is padding the lower limit and is calculating a negative value. This is a "negative" (pun intended) side-effect from prettifying the limits.

Here is a work around, modifying the inverse function to prevent it from accepting a value less than zero, it will avoid the square root of a negative number error.
The lower limit of the axis will always be greater or equal to zero.

library(ggplot2) #square function sq<-function(x){ x^2 } #inverse square function (square root) isq<-function(x){ print(paste("isq",x)) #debug statement x<-ifelse(x<0, 0, x) sqrt(x) } data = data.frame(x = 1:10, y = runif(10), z=rnorm(10, 10)) print(data$y) ggplot(data, aes(x, y, size=z)) + geom_point() + scale_y_continuous(trans=scales::trans_new("sq", sq, isq))

Note: Remove the print function when transferring to production code.

See the link in the comment below for the bug report at Github.

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