r - 将图例添加到 ggplot2 线图

Question

我有一个关于 ggplot2 中的图例的问题。我设法在同一张图中绘制了三条线，并想添加使用三种颜色的图例。这是使用的代码

library(ggplot2)

## edit from original post - removed lines that downloaded data from broken link. Data snippet now below.
## Here a subset as used by [Brian Diggs in their answer](https://stackoverflow.com/a/10355844/7941188)
datos <- structure(list(fecha = structure(c(1317452400, 1317538800, 1317625200, 1317711600, 1317798000, 1317884400, 1317970800, 1318057200, 1318143600, 1318230000, 1318316400, 1318402800, 1318489200, 1318575600, 1318662000, 1318748400, 1318834800, 1318921200, 1319007600, 1319094000), class = c("POSIXct", "POSIXt"), tzone = ""), TempMax = c(26.58, 27.78, 27.9, 27.44, 30.9, 30.44, 27.57, 25.71, 25.98, 26.84, 33.58, 30.7, 31.3, 27.18, 26.58, 26.18, 25.19, 24.19, 27.65, 23.92), TempMedia = c(22.88, 22.87, 22.41, 21.63, 22.43, 22.29, 21.89, 20.52, 19.71, 20.73, 23.51, 23.13, 22.95, 21.95, 21.91, 20.72, 20.45, 19.42, 19.97, 19.61), TempMin = c(
  19.34, 19.14, 18.34, 17.49, 16.75, 16.75, 16.88, 16.82, 14.82, 16.01, 16.88, 17.55, 16.75, 17.22, 19.01,
  16.95, 17.55, 15.21, 14.22, 16.42
)), .Names = c(
  "fecha", "TempMax",
  "TempMedia", "TempMin"
), row.names = c(NA, 20L), class = "data.frame")

ggplot(data = datos, aes(x = fecha, y = TempMax, colour = "1")) +
  geom_line(colour = "red") +
  geom_line(aes(x = fecha, y = TempMedia, colour = "2"), colour = "green") +
  geom_line(aes(x = fecha, y = TempMin, colour = "2"), colour = "blue") +
  scale_y_continuous(limits = c(-10, 40)) +
  scale_colour_manual(values = c("red", "green", "blue")) +
  labs(title = "TITULO", x = NULL, y = "Temperatura (C)") 

我想添加一个图例，其中包含所使用的三种颜色和变量名称(TempMax、TempMedia 和 TempMin)。我努力了scale_colour_manual，但找不到确切的方法。

Answer 1

自 @Etienne当被问及如何在不熔化数据的情况下做到这一点(这通常是首选方法，但我认识到在某些情况下这是不可能的)，我提出了以下替代方案。

从原始数据的子集开始:

datos <-
structure(list(fecha = structure(c(1317452400, 1317538800, 1317625200, 
1317711600, 1317798000, 1317884400, 1317970800, 1318057200, 1318143600, 
1318230000, 1318316400, 1318402800, 1318489200, 1318575600, 1318662000, 
1318748400, 1318834800, 1318921200, 1319007600, 1319094000), class = c("POSIXct", 
"POSIXt"), tzone = ""), TempMax = c(26.58, 27.78, 27.9, 27.44, 
30.9, 30.44, 27.57, 25.71, 25.98, 26.84, 33.58, 30.7, 31.3, 27.18, 
26.58, 26.18, 25.19, 24.19, 27.65, 23.92), TempMedia = c(22.88, 
22.87, 22.41, 21.63, 22.43, 22.29, 21.89, 20.52, 19.71, 20.73, 
23.51, 23.13, 22.95, 21.95, 21.91, 20.72, 20.45, 19.42, 19.97, 
19.61), TempMin = c(19.34, 19.14, 18.34, 17.49, 16.75, 16.75, 
16.88, 16.82, 14.82, 16.01, 16.88, 17.55, 16.75, 17.22, 19.01, 
16.95, 17.55, 15.21, 14.22, 16.42)), .Names = c("fecha", "TempMax", 
"TempMedia", "TempMin"), row.names = c(NA, 20L), class = "data.frame")

您可以通过以下方式获得所需的效果(这也清理了原始绘图代码):

ggplot(data = datos, aes(x = fecha)) +
  geom_line(aes(y = TempMax, colour = "TempMax")) +
  geom_line(aes(y = TempMedia, colour = "TempMedia")) +
  geom_line(aes(y = TempMin, colour = "TempMin")) +
  scale_colour_manual("", 
                      breaks = c("TempMax", "TempMedia", "TempMin"),
                      values = c("red", "green", "blue")) +
  xlab(" ") +
  scale_y_continuous("Temperatura (C)", limits = c(-10,40)) + 
  labs(title="TITULO")

这个想法是通过将颜色美学映射到常量字符串来为每行赋予一种颜色。选择您想要在图例中显示的字符串是最简单的。在本例中，它与绘制的 y 变量的名称相同这一事实并不重要；它可以是任何字符串集。这是非常重要的，这是在 aes 调用中；您正在创建到此“变量”的映射。

scale_colour_manual 现在可以将这些字符串映射到适当的颜色。结果是

在某些情况下，需要通过在手动比例中命名值来明确级别和颜色之间的映射(感谢 @DaveRGP 指出这一点):

ggplot(data = datos, aes(x = fecha)) +
  geom_line(aes(y = TempMax, colour = "TempMax")) +
  geom_line(aes(y = TempMedia, colour = "TempMedia")) +
  geom_line(aes(y = TempMin, colour = "TempMin")) +
  scale_colour_manual("", 
                      values = c("TempMedia"="green", "TempMax"="red", 
                                 "TempMin"="blue")) +
  xlab(" ") +
  scale_y_continuous("Temperatura (C)", limits = c(-10,40)) + 
  labs(title="TITULO")

(给出与之前相同的数字)。对于命名值，可以使用分隔符来设置图例中的顺序，并且可以在值中使用任何顺序。

ggplot(data = datos, aes(x = fecha)) +
  geom_line(aes(y = TempMax, colour = "TempMax")) +
  geom_line(aes(y = TempMedia, colour = "TempMedia")) +
  geom_line(aes(y = TempMin, colour = "TempMin")) +
  scale_colour_manual("", 
                      breaks = c("TempMedia", "TempMax", "TempMin"),
                      values = c("TempMedia"="green", "TempMax"="red", 
                                 "TempMin"="blue")) +
  xlab(" ") +
  scale_y_continuous("Temperatura (C)", limits = c(-10,40)) + 
  labs(title="TITULO")