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Square-root transforms happily inverse-transforms negative values #214

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paleolimbot opened this issue Jun 25, 2019 · 3 comments
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Square-root transforms happily inverse-transforms negative values #214

paleolimbot opened this issue Jun 25, 2019 · 3 comments
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bug an unexpected problem or unintended behavior

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@paleolimbot
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I'm not sure if this should be fixed, but it does lead to some confusing behaviour (tidyverse/ggplot2#980):

library(scales)

trans <- sqrt_trans()
trans$inverse(-2)
#> [1] 4
trans$transform(4)
#> [1] 2

trans <- sqrt_trans()
trans$inverse(-2)
#> [1] 4

# this is what I would expect to happen
trans2 <- trans_new("sqrt2", sqrt, function(x) ifelse(x < 0, NA_real_, x^2), domain = c(0, Inf))
trans2$inverse(-2)
#> [1] NA

Created on 2019-06-25 by the reprex package (v0.2.1)
@hadley hadley closed this as completed in 7fe1b7f Oct 25, 2019
@hadley
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hadley commented Nov 5, 2019

Reverting the fix because it causes a failure in ggplot2

@hadley hadley reopened this Nov 5, 2019
@zeehio
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zeehio commented Nov 19, 2019 •
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I would expect something like sign(x) * sqrt(abs(x)) with a reverse transform like sign(x)*x^2.

Edit: I just saw Hadley had the same idea on the ggplot2 issue

Edit2: I want to add that I would find a sqrt scale that handles negative values useful for visualization purposes regardless of the linked ggplot2 issue.

@hadley hadley added the bug an unexpected problem or unintended behavior label Apr 3, 2020
This was referenced Jul 16, 2020
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@thomasp85
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Changes in ggplot2 means we can now reapply the fix

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@hadley @zeehio @thomasp85 @paleolimbot