Barplot for two groups using ggplot2

Question

I know this has been asked many times before. However, I can't find the solution for my problem.

I extended the mtcars data set by a dummy indicating whether the car was sold or bought by a car seller (buy = 0 -> Sell, buy = 1 -> Buy) and the date of the transaction:

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'))

Now I want to use ggplot to get a barplot with the monthly sells and buys as separate bars. However, I can only create a summary plot of all transactions:

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

How can I create the same graph, but with two bars for each month (one with the number of buys and the other with the number of sells)?

Thanks for your help!

Stephen Ingram · Accepted Answer · 2016-02-13 13:11:54Z

1

I believe the buy vector needs to be strings instead of numbers.

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

edited Feb 13, 2016 at 13:11

answered Feb 13, 2016 at 12:53

Stephen Ingram

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