Make geom_col() ignore data$width

[yutannihilation]

Fix #3142

Currently, geom_bar() does ignore width mapping, but geom_col() does not. Here's my thinking:

• We want to enforce a constant bar width within a panel, so width cannot be an aesthetic.
• Yet, the widths can vary among panels, so we need to pass widths per bar via data, not a single value via param.
• data$width should be used only when it's a calculated value by Stat. But, as geom_col() is not the case, it should ignore data$width.

Note that, this doesn't prevent variable widths when geom_bar() uses such Stat as

• StatIdentity
• some Stat that actually returns variable widths

but I think geom_col() should ignore width for consistency at least.

Current HEAD

library(ggplot2)
library(patchwork)

d <- data.frame(x = c(1,2,3,3,3))

p1 <- ggplot(d) + geom_bar(aes(x, width = x / 2), alpha = 0.7) + ggtitle("bar")
#> Warning: Ignoring unknown aesthetics: width
p2 <- ggplot(d) + geom_col(aes(x, x, width = x / 2), alpha = 0.7) + ggtitle("col")
#> Warning: Ignoring unknown aesthetics: width

p1 / p2
#> Warning: position_stack requires non-overlapping x intervals

^{Created on 2019-03-19 by the reprex package (v0.2.1.9000)}

This PR

library(ggplot2)
library(patchwork)

d <- data.frame(x = c(1,2,3,3,3))

p1 <- ggplot(d) + geom_bar(aes(x, width = x / 2), alpha = 0.7) + ggtitle("bar")
#> Warning: Ignoring unknown aesthetics: width
p2 <- ggplot(d) + geom_col(aes(x, x, width = x / 2), alpha = 0.7) + ggtitle("col")
#> Warning: Ignoring unknown aesthetics: width

p1 / p2

^{Created on 2019-03-19 by the reprex package (v0.2.1.9000)}

[clauswilke]

Do you want to mention in the documentation that geom_col() enforces equal column widths?

[clauswilke]

Just wanted to point out that if somebody writes code such as stat_bin(geom = "col") they could arrive here with a calculated width column, but that would probably be considered inappropriate use then. May be worth a mention in the comment, for the future.

[yutannihilation]

Sure.

[yutannihilation]

Do you want to mention in the documentation that geom_col() enforces equal column widths?

Yes, I think it's good to have it documented clearly.

[yutannihilation]

Hmmm, sorry, after thinking about stat_bin(geom = "col"), now I feel this PR just creates another inconsistency. Let me withdraw this. Really sorry for taking your time, Claus.

To fix this, I think we need to remove data$width from geom_bar() too, but we don't have any measure to propagate calculated widths from a Stat to a Geom other than data (for now).

library(ggplot2)

ggplot(diamonds) +
  stat_bin(aes(carat, width = stat(count)), geom = "col") 
#> Warning: Ignoring unknown aesthetics: width
#> `stat_bin()` using `bins = 30`. Pick better value with `binwidth`.

ggplot(diamonds) +
  stat_bin(aes(carat, width = stat(count)), geom = "bar") 
#> Warning: Ignoring unknown aesthetics: width
#> `stat_bin()` using `bins = 30`. Pick better value with `binwidth`.
#> Warning: position_stack requires non-overlapping x intervals

^{Created on 2019-03-22 by the reprex package (v0.2.1)}

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