ggplot2繪圖系統——坐標軸調節
scale函數：圖形遙控器。坐標軸標度函數：
scale_x_continous
scale_y_continous
scale_x_discrete
scale_y_discrete
1. 連續型變量坐標軸
函數及其參數：
scale_x_continuous(name = , #坐標軸標簽
breaks = , #定義刻度
minor_breaks = ,
labels = , #刻度標簽
limits = ,
expand = c(0.05,0),
#坐標軸延伸，確保圖形元素不覆蓋坐標
oob = censor,#識別越過邊界的點
na.value = NA_real_,
trans = 'identity', #統計變換
position = 'bottom', #left/right/top
sec.axis = #定義第二坐標軸
)
統計變換參數備選：asn/atanh/boxcox/exp/identity/log/log10/log1p/log2/logit/probability/probit/reciprocal/reverse/sqrt
p1 <- ggplot(mpg,aes(displ,hwy))+geom_point()
a=p1+scale_x_continuous('L')+ #同xlab
scale_y_continuous("H")
b=p1+scale_x_continuous(limits = c(0,10)) #同xlim
c=p1+scale_x_continuous(breaks = c(2,4,6),
labels = c('two','four','six'))
gridExtra::grid.arrange(a,b,c,ncol=3)
刻度標簽轉化為百分比
調用scales包中的percent函數。
prop <- data.frame(sex=rep(c('Male','Female'),each=5),
age=rep(c('0-14','15-34','35-49','50-64','65+'),2),
prop=c(0.12,0.37,0.23,0.17,0.11,0.09,0.33,0.28,0.21,0.09))
ggplot(prop,aes(x=age,weight=prop,fill=sex))+
geom_bar(position = 'dodge')+
scale_y_continuous(labels = scales::percent)+
ylab('Proportion')
2. 離散型坐標軸
針對離散型變量，在條形圖、盒形圖中使用較多。
d <- ggplot(subset(diamonds,carat>1),aes(cut,clarity))+
geom_jitter()
#重定義坐標軸標簽
a=d+scale_x_discrete('Cut',labels=c('Fair'='F','Good'='G','Very Good'='VG',
'Premium'='P','Ideal'="I"))
#取值范圍，這里相當於取子集
b=d+scale_x_discrete(limits=c('Fair','Ideal'))
grid.arrange(a,b,nrow=1)
ggplot(mpg,aes(reorder(manufacturer,displ),cty))+
geom_point()+
scale_x_discrete(labels=abbreviate)
#abbreviate函數縮寫x軸標簽
3. theme函數調節坐標軸
標度函數和theme調節坐標軸分工稍有不同，前者用於框架搭建，后者用於細節修飾。
theme修飾坐標軸常用參數：
應用示例。
p <- ggplot(mtcars,aes(mpg,wt))+geom_point()
p+theme(axis.title = element_text(color = 'red',size=18),
axis.line = element_line(color='blue'),
axis.text = element_text(color = 'orange',size = 12),
axis.ticks = element_line(color = 'light skyblue',size=3))
theme主題函數本身不具備生成功能。即不能生成一個坐標軸標簽，只能在現有標簽基礎上進行修飾。