geom_rect and ggplot2 Error: Aesthetics must be either length 1 or the same as the data (2)

Question

I am trying to do something like https://stackoverflow.com/a/29649406/15485 but I get the error

Error: Aesthetics must be either length 1 or the same as the data (2): xmin, xmax, ymin, ymax, x, y

What does '(2)' means?

What 'Aesthetics' are involved? I have aes in ggplot and aes in geom_rect but I have no idea about how to correct them... I am afraid I will never grasp ggplot...

days<-rep(Sys.Date(),100)+seq(1,100)
v<-sin(as.numeric(days))
df<-data.frame(days=days,v=v)

shade <- data.frame(x1=c(as.Date('2017-10-15'),as.Date('2017-11-11')), 
                   x2=c(as.Date('2017-10-20'),as.Date('2017-11-13')), 
                   y1=c(-Inf,-Inf), y2=c(Inf,Inf))

library(ggplot2)
plot(ggplot(df,aes(x=days,y=v))
     +geom_line()
     +geom_rect(data=shade, 
               mapping=aes(xmin=x1, xmax=x2, ymin=y1, ymax=y2), color='grey', alpha=0.2)
     +geom_point())

Answer 1

The geom_rect line was trying to inherit default aesthetics from the top line ggplot(df, aes(x = days, y = v)).

The following would work:

ggplot(df, aes(x=days, y=v)) +
  geom_line() +
  geom_rect(data=shade, inherit.aes = F,
            aes(xmin=x1, xmax=x2, ymin=y1, ymax=y2), 
            color = 'grey', alpha=0.2) +
  geom_point()

(I added more line breaks / spaces into the code for easier reading. Also, there's no need to wrap the whole ggplot object in plot().)