本文介绍了ggplot2:scale_alpha()的阈值的处理方法,对大家解决问题具有一定的参考价值,需要的朋友们下面随着小编来一起学习吧!
问题描述
是否可以为颜色范围指定阈值?
Is it possible to specify thresholds for color-scales?
查看此示例:
xy <- expand.grid(x=1:20,y=1:20)
xyd <- data.frame(xy,z=runif(400),a=rowSums(xy)/40)
g <- ggplot(xyd, aes(x=x, y=y, fill=z, alpha=a)) +
geom_tile() +
scale_alpha(range=c(0,1), limits=c(0.5,1))
g
$ b b
我想要的是,a值低于0.5时,alpha值为0,因此左下半部分将不可见。显然,我可以转换原始数据,但会破坏传说。
What I want is that Values of a below 0.5 get an alpha value of 0 so that the lower left half will be invisible. Obviously I could transform the original data but that would destroy the legend.
推荐答案
阈值是工作,设置为 NA
;问题是 alpha
的 NA
正在呈现为完全不透明度。将 na.value
设置为 0
可获得所需的结果。
The threshold is working and the values outside that threshold are set to NA
; the problem is that an alpha
of NA
is getting rendered as full opacity. Setting the na.value
on the scale to 0
gets the results you want.
ggplot(xyd, aes(x=x, y=y, fill=z, alpha=a)) +
geom_tile() +
scale_alpha(range=c(0,1), limits=c(0.5,1), na.value = 0)
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