我们经常会遇到这种情况：需要把特定的坐标轴标签用不同的颜色进行高亮。
例如我们画这么一幅图：1
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14x <- c("a","b","c","d","e","f")
y <- c("10", "9","-10","11","-3","-15")
data <- data.frame(x, y)
data$y <- as.numeric(as.character(data$y))
data$category <- ifelse(as.numeric(data$y)<0, 0, 1)
data$category <- as.factor(data$category)
#Graph
library(cowplot) #theme
library(ggplot2)
ggplot(data, aes(x=x, y=y)) +
geom_bar(stat = "identity", aes(fill=category)) +
theme(axis.text.x = element_text(angle = 45, hjust = 1)) +
theme(axis.text.x = element_text(colour = "black"))
这个画图里面用到了一个比较抽象的ifelse()函数，该函数1
ifelse(b,u,v)
其中b是一个布尔向量，通常为一个判断值，u和v为向量。如果b[i]为真，则返回的第i个与秦素为u[i],如果b[i]为假，则返回的第i个元素为v[i]。例如：1
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6> x <- 1:10
> x
[1] 1 2 3 4 5 6 7 8 9 10
> y <- ifelse(x %% 2==0,5,12)
> y
[1] 12 5 12 5 12 5 12 5 12 5 ###如果能被2整除，则返回5，如果不能则返回12
然而如果我们想将x轴小于0的标签标为红色，应该如何操作？
可以先根据data$category来进行判断，指定每个向量的颜色：1
a <- ifelse(data$category == 0, "red", "blue")
然后1
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3ggplot(data, aes(x = x, y = y)) +
geom_bar(stat = "identity", aes(fill = category)) +
theme(axis.text.x = element_text(angle = 45, hjust = 1, colour = a))
其中向量a的内容如下：1
2> a
[1] "blue" "blue" "red" "blue" "red" "red"
其中theme()中的colour=a是将a这个指定颜色的向量透射到colour上,于是生成如下的图：
完整代码：1
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16x <- c("a","b","c","d","e","f")
y <- c("10", "9","-10","11","-3","-15")
data <- data.frame(x, y)
data$y <- as.numeric(as.character(data$y))
data$category <- ifelse(as.numeric(data$y)<0, 0, 1)
data$category <- as.factor(data$category)
#Graph
library(cowplot) #theme
library(ggplot2)
a <- ifelse(data$category == 0, "red", "blue")
ggplot(data, aes(x = x, y = y)) +
geom_bar(stat = "identity", aes(fill = category)) +
theme(axis.text.x = element_text(angle = 45, hjust = 1, colour = a))
参考：