This function adds position scales (x and y) of individual panels. These can be used to fine-tune limits, breaks and other scale parameters for individual panels, provided the facet allows free scales.

## Arguments

- expr
An

`expression`

that, when evaluated in the facet's layout data.frame, yields a`logical`

vector. See details.- ...
Other arguments passed to the scale.

- type
A

`character(1)`

indicating the type of scale, such that`scale_(x/y)_{type}`

spells a scale function. Defaults to`"continuous"`

.

## Details

These scale functions work through the mechanism of the
`facetted_pos_scales()`

function, and the same limitations apply: scale
transformations are applied after `stat`

transformations, and the `oob`

argument of scales is ignored.

For the `expr`

argument, the expression will be evaluated in the context
of the plot's layout. This is an internal `data.frame`

structure that
isn't normally exposed, so it requires some extra knowledge. For most
facets, the layout describes the panels, with one panel per row. It
typically has `COL`

, `ROW`

and `PANEL`

columns that keep track of what
panel goes where in a grid of cells. In addition, it contains the
facetting variables provided to the `facets`

or `rows`

and `cols`

arguments
of the facets. For example, if we have a plot facetted on the `var`

variable with the levels `A`

, `B`

and `C`

, as 1 row and 3 columns, we might
target the second `B`

panel with any of these expressions: `var == "B"`

,
`PANEL == 2`

or `COL == 2`

. We can inspect the layout structure by using
`ggplot_build(p)$layout$layout`

, wherein `p`

is a plot.

When using multiple `scale_(x/y)_facet()`

, the `expr`

argument can target
the same panels. In such case, the scales added to the plot first overrule
the scales that were added later.

## See also

The `facetted_pos_scales()`

function.

## Examples

```
# A standard plot with continuous scales
p <- ggplot(mtcars, aes(disp, mpg)) +
geom_point() +
facet_wrap(~ cyl, scales = "free")
# Adding a scale for a value for a facetting variable
p + scale_x_facet(cyl == 8, limits = c(200, 600))
# Adding a scale by position in the layout
p + scale_x_facet(COL == 3, limits = c(200, 600))
# Setting the default scale and making an exception for one panel
p + scale_y_continuous(limits = c(0, 40)) +
scale_y_facet(PANEL == 1, limits = c(10, 50))
# Using multiple panel-specific scales
p + scale_y_facet(PANEL == 1, limits = c(10, 50)) +
scale_y_facet(cyl == 6, breaks = scales::breaks_width(0.5))
# When multiple scales target the same panel, the scale added first gets
# priority over scales added later.
p + scale_y_facet(COL == 2, limits = c(10, 40)) +
scale_y_facet(cyl %in% c(4, 6), breaks = scales::breaks_width(1))
# A standard plot with discrete x scales
p <- ggplot(mtcars, aes(factor(cyl), mpg)) +
geom_boxplot() +
facet_wrap(~ vs, scales = "free")
# Expanding limits to show every level
p + scale_x_facet(vs == 1, limits = factor(c(4, 6, 8)), type = "discrete")
# Shrinking limits to hide a level
p + scale_x_facet(vs == 0, limits = factor(c(4, 6)), type = "discrete")
#> Warning: Removed 14 rows containing missing values or values outside the scale range
#> (`stat_boxplot()`).
```