barplot兩組使用ggplot2

Question

我知道這已被問了很多次之前。但是，我無法找到解決問題的方案。

我延長mtcars數據由虛設設定表示轎廂是否被出售或由車賣方購買（購買= 0 - >產品信息，購買= 1 - >買）和交易日期：

data(mtcars) 
mtcars$buy <- c(0,0,1,0,0,1,1,0,0,1,0,1,0,0,0,1,1,0,0,0,1,0,1,0,1,1,0,0,0,1,0,1) 
mtcars$date <- as.Date(c('2011-01-01','2011-01-06','2011-01-10','2011-01-20','2011-01-23', 
      '2011-01-25','2011-01-31','2011-02-01','2011-02-06','2011-02-15', 
      '2011-02-22','2011-02-26','2011-03-05','2011-03-15','2011-03-20', 
      '2011-03-22','2011-03-27','2011-04-10','2011-04-25','2011-04-28', 
      '2011-05-05','2011-05-15','2011-06-05','2011-06-06','2011-06-17', 
      '2011-06-25','2011-07-05','2011-07-11','2011-07-25','2011-07-31', 
      '2011-08-23','2011-08-25')) 

現在我想用ggplot來獲得一個每月賣出和作爲單獨條形圖購買的barplot。但是，我只能創建的所有事務的總括圖：

mtcars$month <- as.Date(cut(mtcars$date, breaks="month")) 
mtcars$counter <- 1 
ggplot(mtcars, aes(month,counter)) + stat_summary(fun.y=sum, geom="Bar") 

如何創建相同的圖形，但兩間酒吧每個月（一個購買的數量和其他與賣出數量）？

感謝您的幫助！

Answer 1

我相信購買矢量需要字符串而不是數字。

ggplot(mtcars, aes(month)) + geom_bar(aes(fill=as.character(buy)),position = "dodge")