trouble with unit arithmetics #789

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ringprince opened this Issue Mar 26, 2013 · 2 comments

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Setting the margin using unit arithmetics fails

Example:

library("ggplot2")
library("grid")

p <- ggplot(mpg, aes(displ, hwy)) + geom_point()

margin1 <-
  unit(c(0.5, 1, 0.5, 1),
       c("lines", "lines", "lines", "strwidth"),
       data=list(NULL, NULL, NULL, "uplrp"))

margin2 <-
  unit(c(0, 0, 0, 1),
       c("lines", "lines", "lines", "strwidth"),
       data=list(NULL, NULL, NULL, "1.00"))

margin3 <- margin1-margin2

margin3                                ## valid

p + theme(plot.margin=margin1)         ## works
p + theme(plot.margin=margin2)         ## works
p + theme(plot.margin=margin3)         ## does not work

I got an Email from Paul Murrel:

that is happening because add_theme() tries to do the following to margin3 (where 'y' is margin3) ...

        idx <- !vapply(y, is.null, logical(1))
        idx <- names(idx[idx])
        x[idx] <- y[idx]

... which is not a sensible thing to do with a unit arithmetic object. I would argue that this is a problem with add_theme() trying to do something very generic with the low-level structure of an object that it does not understand and should not be poking around in. That block of code should probably be a generic function, for which it may be necessary to write a 'unit' method.

Owner

hadley commented Feb 24, 2014

This sounds like a great feature/horrible bug, but unfortunately we don't currently have the development bandwidth to support it/fix it. If you'd like to submit a pull request that implements this feature/fixes this bug, please follow the instructions in the development vignette.

hadley closed this Feb 24, 2014

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