ggplot2 图例不起作用/添加手动图例

Question

我是 R 的新手。 图例和绘图似乎比 Python 更难。 如何更改图表以在图例中将每个节点显示为不同的颜色？ 现在我有类似图片的东西。 谢谢您的帮助。

library(ggplot2)
library(MASS)
library(car)
library(robustbase)

data("airquality")
# Select only Ozone and Temp variables
air = airquality[c("Ozone" , "Temp")]
# We need to remove NA from data set
air = na.omit(air)
air.center  = colMeans(air)
air.cov = cov(air)
rad  = sqrt(qchisq(p = 0.95 , df = ncol(air)))
ellipse <- ellipse(center = air.center , shape = air.cov , radius = rad ,
                        segments = 150 , draw = FALSE)

ellipse <- as.data.frame(ellipse)
colnames(ellipse) <- colnames(air)
# Finding distances
distances <- mahalanobis(x = air , center = air.center , cov = air.cov)
# Cutoff value for ditances from Chi-Sqaure Dist. 
# with p = 0.95 df = 2 which in ncol(air)
cutoff <- qchisq(p = 0.95 , df = ncol(air))
### Minimum Covariance Determinant (MCD)
Y_mcd <- covMcd(air)
# Robust estimate of location
Y_mcd$center
# Robust estimate of scatter
Y_mcd$cov
# Make elilipse 
ellipse_mcd <- data.frame(ellipse(center = Y_mcd$center,
                                  shape = Y_mcd$cov,
                                  radius= rad, 
                                  segments=100,draw=FALSE))
#the same names as in previous plot
colnames(ellipse_mcd) <- colnames(air)
plot_fig <- ggplot(air , aes(x = Ozone , y = Temp)) +
  geom_point(size = 2) +
  geom_polygon(data = ellipse , fill = "blue" , color = "blue" , alpha = 0.5,show.legend    =T)+
  geom_point(aes(air.center[1] , air.center[2],fill='Mahalanobis') , size = 5 , color = "blue") +
  geom_text(data=subset(air, distances > cutoff),
            aes(Ozone,Temp,label=row.names(air[distances > cutoff ,])),  hjust = 1 , vjust = -1.5 ,size = 3.5)+
  ylab("Temperature Values") + xlab("Ozone Values")+ggtitle("Mahalanobis distance")+ theme(
    legend.position = c(0.95, 0.15),
    legend.justification = c("right", "top")
  ) + geom_polygon(data=ellipse_mcd,aes(x = Ozone,y = Temp, colour='LINE2'), color="red", fill="red", 
                   alpha=0.3, inherit.aes = FALSE) +
  geom_point(aes(x = Y_mcd$center[1], y = Y_mcd$center[2],fill='MCD'),
             color = "red", size = 6)

plot_fig

Answer 1

问题是您映射了fill美学并将点的颜色设置为 arguments。 而是 map color aes 上的标签并通过scale_color_manual设置颜色值：

plot_fig <- ggplot(air , aes(x = Ozone , y = Temp)) +
  geom_point(size = 2) +
  geom_polygon(data = ellipse , fill = "blue" , color = "blue" , alpha = 0.5, show.legend =T)+
  geom_point(aes(air.center[1] , air.center[2], color = 'Mahalanobis'), size = 5) +
  geom_text(data=subset(air, distances > cutoff),
            aes(Ozone,Temp,label=row.names(air[distances > cutoff ,])),  hjust = 1 , vjust = -1.5 ,size = 3.5)+
  ylab("Temperature Values") + 
  xlab("Ozone Values")+
  ggtitle("Mahalanobis distance")+ 
  theme(
    legend.position = c(0.95, 0.15),
    legend.justification = c("right", "top")
  ) + 
  geom_polygon(data=ellipse_mcd,aes(x = Ozone,y = Temp, colour='LINE2'), color="red", fill="red", 
                   alpha=0.3, inherit.aes = FALSE) +
  geom_point(aes(x = Y_mcd$center[1], y = Y_mcd$center[2], color='MCD'), size = 6) +
  scale_color_manual(values = c(MCD = "red", Mahalanobis = "blue"))

plot_fig

Answer 2

如果您将 Mahalanobis/MCD 分类变量 map 设置为colour ，则让fill取决于映射的颜色，图例应该自然地自行排序，您可以使用scale_colour_manual()设置颜色。

ggplot(air, aes(Ozone, Temp)) +
  geom_point(size = 2) +
  geom_polygon(
    data = ellipse, 
    aes(fill = after_scale(alpha(colour, 0.5)), colour = "Mahalanobis")
  ) +
  geom_polygon(data = ellipse_mcd,
               aes(fill = after_scale(alpha(colour, 0.3)), colour = "MCD")) +
  geom_point(aes(air.center[1], air.center[2], colour = "Mahalanobis"), 
             size = 5) +
  geom_point(aes(Y_mcd$center[1], Y_mcd$center[2], colour = "MCD"), size = 5) +
  geom_text(data = subset(air, distances > cutoff),
            aes(label = row.names(air[distances > cutoff, ])),
            hjust = 1, vjust = -1.5, size = 3.5) +
  scale_colour_manual(values = c("blue", "red")) +
  labs(x = "Ozone Values", y = "Temperature values", 
       title = "Mahalanobis distance") +
  theme(legend.position = c(0.95, 0.15),
        legend.justification = c("right", "top"))