Inconsistency geom_abline <-> geom_hline for log10 transformation

[lcougnaud]

In case a transformation is applied, the geom_hline function takes the intercept in the initial scale, contrary to the other geoms.

p1 <- ggplot(mpg, aes(displ, hwy)) + geom_point() + scale_y_log10()

The line is created if the intercept is specified in the original (non-transformed) scale in geom_hline:

p1 + geom_hline(yintercept = 30)

Contrary to the geom_abline behaviour:

p1 + geom_abline(intercept = log10(30), slope = 0)

[clauswilke]

I suspect this happens because yintercept is recognized as a position aesthetic and automatically transformed whereas intercept is not. The simple solution would be to rename intercept into yintercept, though I'm not too fond of this approach. In general, I'm not too excited about the current mechanism of identifying position aesthetics, because it seems ad-hoc and error-prone. A better approach would allow geoms and stats to identify which aesthetics should be treated as position aesthetics.

[clauswilke]

Here is the code that catches all the y position aesthetics. I guess another fix would be to add intercept in line 105.

ggplot2/R/scale-continuous.r

Lines 97 to 110 in 5e388e1

	scale_y_continuous <- function(name = waiver(), breaks = waiver(),
	minor_breaks = waiver(), n.breaks = NULL,
	labels = waiver(), limits = NULL,
	expand = waiver(), oob = censor,
	na.value = NA_real_, trans = "identity",
	guide = waiver(), position = "left",
	sec.axis = waiver()) {
	sc <- continuous_scale(
	c("y", "ymin", "ymax", "yend", "yintercept", "ymin_final", "ymax_final", "lower", "middle", "upper", "y0"),
	"position_c", identity, name = name, breaks = breaks, n.breaks = n.breaks,
	minor_breaks = minor_breaks, labels = labels, limits = limits,
	expand = expand, oob = oob, na.value = na.value, trans = trans,
	guide = guide, position = position, super = ScaleContinuousPosition
	)

[thomasp85]

I agree with @clauswilke that geom_hline()'s behaviour is correct and it is geom_abline() that needs to be corrected