r - 日付軸Rを持つggplot垂直線

Question

Rでggplotを使用して垂直線をプロットするのに問題があります.

時系列に毎週日曜日に垂直線を引きたい:

VisitDate VisitMonth VisitYear      City   Weekday VisitWeek Code_CxF               Centre  Location
1 2014-05-02           05        2014 Barcelona    05Friday  2014-04-28  CxF_BCN CaixaForum Barcelona Catalunya
2 2014-05-03           05        2014 Barcelona  06Saturday  2014-04-28  CxF_BCN CaixaForum Barcelona Catalunya
3 2014-05-04           05        2014 Barcelona    07Sunday  2014-04-28  CxF_BCN CaixaForum Barcelona Catalunya
4 2014-05-06           05        2014 Barcelona   02Tuesday  2014-05-05  CxF_BCN CaixaForum Barcelona Catalunya
5 2014-05-07           05        2014 Barcelona 03Wednesday  2014-05-05  CxF_BCN CaixaForum Barcelona Catalunya
6 2014-05-08           05        2014 Barcelona  04Thursday  2014-05-05  CxF_BCN CaixaForum Barcelona Catalunya

次の表現を試しました。

ggplot(data = MUSEUS_PLOT, aes(x = VisitDate, y = Visitors.x)) + 
  geom_line(size=0.25, aes(x = VisitDate, y = Visitors.x, colour = "CxF")) + 
  geom_line(aes(y = Visitors.y, colour = "MNAC")) + 
  labs(title = "MONTJUICH May 2014", x = "Day", y = "Visitors") +
  scale_colour_manual(name="Legend",values=c(CxF="darkcyan", MNAC="darkorange2")) +
  geom_vline(aes(xintercept = which(weekdays(MUSEUS_PLOT$VisitDate) == "Sunday")))

しかし、それは機能していません:

Error in data.frame(xintercept = c(3L, 9L, 15L, 21L), PANEL = c(1L, 1L,  : 
  arguments imply differing number of rows: 4, 26

いくつかのアイデア？