y-position of points created with gghalves::geom_half_point() is variable

[alesantuz]

Windows 10 x64, build 19045, x86-64 machine
R version 4.3.1 (2023-06-16 ucrt)

As per title, when plotting individual data points with gghalves::geom_half_point(), the y-position of the points changes at every run, especially when the data set is very small.

MRE:

ggplot2::ggplot(iris, ggplot2::aes(x = Species, y = Petal.Width, fill = Species)) + 
    gghalves::geom_half_point()

Another reproducible example, where the error is amplified by the small data set:

data <- data.frame(
  group = c("1", "2", "2", "1", "2", "2", "2", "2"),
  value = c(0.526, 0.473, 0.505, 0.508, 0.505, 0.488, 0.47, 0.499)
)

ggplot2::ggplot() +
  gghalves::geom_half_point(
    data = (data),
    ggplot2::aes(
      x = .data[["group"]],
      y = .data[["value"]]
    )
  )

[alesantuz]

Is there any update on this issue? I add here a similar MRE as the above, with a couple of pictures:

data <- data.frame(
  group = c("1", "2", "2", "1", "2", "2", "2", "2"),
  value = c(0.526, 0.473, 0.505, 0.508, 0.505, 0.488, 0.47, 0.499)
)

ggplot2::ggplot() +
  ggplot2::coord_cartesian(ylim = c(0.45, 0.55)) +
  gghalves::geom_half_point(
    data = (data),
    ggplot2::aes(
      x = .data[["group"]],
      y = .data[["value"]]
    )
  ) +
  gghalves::geom_half_boxplot(
    data = (data),
    ggplot2::aes(
      x = .data[["group"]],
      y = .data[["value"]]
    )
  )

In the following screenshots it is possible to see that the position of the individual data points is wrong and changes with every run, especially when there are only few points:

[erocoar]

@alesantuz Apologies for the long silence- it's difficult when life gets in the way. I promise to review this over the next few days 😊

[alesantuz]

Thanks @erocoar!

[aboggio-pasqua]

Hi @erocoar! Any update on this issue? I have exactly the same problem... Thanks 😊

[Neurarian]

This happens due to position_jitter() jittering both vertically and horizontally by default. You can avoid this by supplying transformation = position_jitter(height = 0) to the transformation argument of the geom_half_point() function instead of relying on the default.

data <- data.frame(
  group = c("1", "2", "2", "1", "2", "2", "2", "2"),
  value = c(0.526, 0.473, 0.505, 0.508, 0.505, 0.488, 0.47, 0.499)
)

ggplot2::ggplot() +
  gghalves::geom_half_point(
    data = (data),
    transformation = ggplot2::position_jitter(height = 0),
    ggplot2::aes(
      x = .data[["group"]],
      y = .data[["value"]]
    )
  )

If jittering in y should not occur by default, I could open a pull request and set height = 0 as a more sensible setting.

[alesantuz]

Thank you very much @Neurarian! Yeah, I really think it shouldn't happen by default, as we aim to show the true values here, not random dots. And I agree that height = 0 seems like a sensible default.