如何从 ggplot 对象中提取填充颜色? [英] How to extract the fill colours from a ggplot object?
问题描述
我正在尝试为一系列生成 ggplot
图形的函数编写一些自动化单元测试.
I am trying to write some automated unit tests for a series of functions that generates ggplot
graphics.
例如,我想为绘图设置特定的色标.现在我需要一种方法来确定是否实际应用了正确的色阶.
For example, I want to set a specific colour scale to a plot. Now I need a way to determine whether the correct colour scale was actually applied.
这是一些示例代码,设置fill
颜色以使用ColourBrewer调色板Dark2
:
Here is some example code, that set the fill
colour to use the ColourBrewer palette Dark2
:
p <- ggplot(mtcars, aes(x=factor(cyl), y=mpg, fill=factor(gear))) +
geom_bar(stat="identity") +
facet_grid(~gear) +
scale_fill_brewer(palette="Dark2")
print(p)
好的,目视检查告诉我代码有效.
OK, so a visual inspection tells me the code worked.
现在我想通过检查对象来确认这一点:
Now I want to confirm this by inspecting the object:
str(p, max.level=1)
List of 8
$ data :'data.frame': 32 obs. of 11 variables:
$ layers :List of 1
$ scales :Reference class 'Scales' [package "ggplot2"] with 1 fields
..and 20 methods, of which 9 are possibly relevant
$ mapping :List of 3
$ options :List of 1
$ coordinates:List of 1
..- attr(*, "class")= chr [1:2] "cartesian" "coord"
$ facet :List of 9
..- attr(*, "class")= chr [1:2] "grid" "facet"
$ plot_env :<environment: R_GlobalEnv>
- attr(*, "class")= chr "ggplot"
好吧,$scales
对象看起来很有趣.让我们更详细地了解一下:
Fine, the $scales
object seems interesting. Let's look at that in more detail:
str(p$scales)
Reference class 'Scales' [package "ggplot2"] with 1 fields
$ scales:List of 1
..$ :List of 14
.. ..$ call : language discrete_scale(aesthetics = "fill", scale_name = "brewer", palette = brewer_pal(type, palette))
.. ..$ aesthetics: chr "fill"
.. ..$ scale_name: chr "brewer"
.. ..$ palette :function (n)
.. ..$ range :Reference class 'DiscreteRange' [package "scales"] with 1 fields
.. .. ..$ range: NULL
.. .. ..and 14 methods, of which 3 are possibly relevant:
.. .. .. initialize, reset, train
.. ..$ limits : NULL
.. ..$ na.value : logi NA
.. ..$ expand : list()
.. .. ..- attr(*, "class")= chr "waiver"
.. ..$ name : NULL
.. ..$ breaks : list()
.. .. ..- attr(*, "class")= chr "waiver"
.. ..$ labels : list()
.. .. ..- attr(*, "class")= chr "waiver"
.. ..$ legend : NULL
.. ..$ drop : logi TRUE
.. ..$ guide : chr "legend"
.. ..- attr(*, "class")= chr [1:3] "brewer" "discrete" "scale"
and 20 methods, of which 9 are possibly relevant:
add, clone, find, get_scales, has_scale, initialize, input, n, non_position_scales
但在这里我画了一个空白.p$scales
中没有任何东西看起来像我的输入 palette
,或者实际上像颜色.
But here I draw a blank. There is nothing inside p$scales
that looks like either my input palette
, or in fact like colours.
我期望的颜色是:
library(RColorBrewer)
brewer.pal(3, name="Dark2")
[1] "#1B9E77" "#D95F02" "#7570B3"
问题:
如何查询 ggplot
对象以获取要使用的特定填充颜色?
The question:
How do I interrogate a ggplot
object for specific fill colours to use?
推荐答案
尝试构建情节,
g <- ggplot_build(p)
unique(g$data[[1]]["fill"])
fill
1 #1B9E77
16 #D95F02
28 #7570B3
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