r - 在facet_wrap的某些面板上的geom_rect

Question

我正在尝试在facet_wrap图的前三个面板上获得一个阴影矩形。但是，当我使用geom_rect进行作业时，它将在每个面板上产生矩形。有没有办法只在前三个面板上有选择地获取矩形？

这是一些代码

dfTemp = data.frame(value = rnorm(100*4), variable = sort(rep(1:4, 100)),
                    date = rep(seq.Date(
                      from = as.Date('2011-01-01', format = '%Y-%m-%d'),
                      length.out = 100,
                      by = 'day'), 4))

ggplot(dfTemp) +
  geom_rect(aes(xmin = as.Date('2011-02-01', format = '%Y-%m-%d'),
                xmax = as.Date('2011-03-01', format = '%Y-%m-%d'),
                ymin = -Inf,
                ymax = Inf), alpha = 0.2, fill = 'grey') +
  geom_line(aes(x = date, y = value, group = variable, color = factor(variable))) +
  facet_wrap(~variable , scale = 'free', ncol = 1) 

更新1:

我将代码更新为

dfTemp = data.frame(value = rnorm(100*4), variable = sort(rep(1:4, 100)),
                    date = rep(seq.Date(
                      from = as.Date('2011-01-01', format = '%Y-%m-%d'),
                      length.out = 100,
                      by = 'day'), 4))

ggplot(dfTemp) +
  geom_rect(data = dfTemp[dfTemp$variable %in% c(2, 3),],
            aes(xmin = as.Date('2011-02-01', format = '%Y-%m-%d'),
                xmax = as.Date('2011-03-01', format = '%Y-%m-%d'),
                ymin = -Inf,
                ymax = Inf), alpha = 0.2, fill = 'grey') +
  geom_line(aes(x = date, y = value, group = variable, color = factor(variable))) +
  facet_wrap(~variable , scale = 'free', ncol = 1) 

请注意，我现在将要传递给 geom_rect的数据设置为子集。但这给了我这个警告:

Warning message: In [<-.factor(*tmp*, rng, value = c(1L, 1L, 1L, 1L, 1L, 1L, : invalid factor level, NA generated

这是什么意思？

Answer 1

这是一个使用variable创建新数据帧，然后利用aes中的回收来为variable中的每个值生成矩形坐标的解决方案。

ggplot(dfTemp) +
  geom_rect(
    data=data.frame(variable=factor(1:3)), 
    aes(xmin=as.Date('2011-02-01'), xmax=as.Date('2011-03-01'), ymin=-Inf, ymax=Inf), 
    alpha = 0.5, fill = 'grey') +
  geom_line(aes(x = date, y = value, group = variable, color = factor(variable))) +
  facet_wrap(~variable , scale = 'free', ncol = 2)