r - ggplot2 基于不同数据集的两个图例

Question

ggplot2 是否可以有两个图例但基于不同的数据集？例如，在下面的代码中，我想在同一张图中同时获取第一种情况的图例和第二种情况的图例。我的尝试（第三种情况）不起作用。

library(ggplot2)
library(scales)

yrng <- range(economics$unemploy)
xrng <- range(economics$date)
presidential <- presidential[-(1:3), ]

# add a fictive factor to the economics dataset
economics <- cbind.data.frame(economics, col=gl(2, nrow(economics)/2))

#####################
## first situation ##
#####################
# first plot with legend
unemp <- qplot(date, unemploy, data=economics, geom="line",
                 xlab = "", ylab = "No. unemployed (1000s)", colour=col)
# second plot without legend
unemp + geom_vline(aes(xintercept = start), data = presidential)

######################
## second situation ##
######################
# first plot without legend
unemp <- qplot(date, unemploy, data=economics, geom="line",
                 xlab = "", ylab = "No. unemployed (1000s)")
# second plot with legend
unemp + 
  geom_rect(aes(NULL, NULL, xmin = start, xmax = end,
                    fill = party), ymin = yrng[1], ymax = yrng[2],
                    data = presidential) +
  scale_fill_manual(values = alpha(c("blue", "red"), 0.2))


#####################
## third situation ##
#####################
# first plot with legend
unemp <- qplot(date, unemploy, data=economics, geom="line",
                 xlab = "", ylab = "No. unemployed (1000s)", colour=col)
# second plot with legend
unemp + 
  geom_rect(aes(NULL, NULL, xmin = start, xmax = end, fill = party), ymin = yrng[1],
              ymax = yrng[2], data = presidential) + 
  scale_fill_manual(values = alpha(c("blue", "red"), 0.2))

Error in data.frame(xmin = 11342, xmax = 14264, fill = "Republican", colour = function   (x,  : 
  arguments imply differing number of rows: 1, 0

Answer 1

一般来说，一旦我开始处理更复杂的情节，停止使用qplot并改用它几乎总是更好ggplot。我发现更容易思考我是如何逐步构建情节的：

ggplot() +
  geom_line(aes(x=date, y=unemploy, color=col), data=economics) +
  geom_rect(aes(xmin=start, xmax=end, fill=party),
            ymin = yrng[1], ymax = yrng[2], data = presidential) +
  scale_fill_manual(values = alpha(c("blue", "red"), 0.2)) +           
  xlab("") +
  ylab("No. unemployed (1000s)")

这给出了：