ggplot2 + Date structure using scale X - r

Question

I really need help here because I am way beyond lost.
I am trying to create a line chart showing several teams' performance over a year. I divided the year into quarters: 1/1/2012, 4/1/12. 8/1/12. 12/1/12 and loaded the csv data frame into R.
Month Team Position
1 1/1/12 South Africa 56
2 1/1/12 Angola 85
3 1/1/12 Morocco 61
4 1/1/12 Cape Verde Islands 58
5 4/1/12 South Africa 71
6 4/1/12 Angola 78
7 4/1/12 Morocco 62
8 4/1/12 Cape Verde Islands 76
9 8/1/12 South Africa 67
10 8/1/12 Angola 85
11 8/1/12 Morocco 68
12 8/1/12 Cape Verde Islands 78
13 12/1/12 South Africa 87
14 12/1/12 Angola 84
15 12/1/12 Morocco 72
16 12/1/12 Cape Verde Islands 69
When I try using ggplot2 to generate the graph the fourth quarter 12/1/12 inexplicably moves to the second spot.
ggplot(groupA, aes(x=Month, y=Position, colour=Team, group=Team)) + geom_line()
I then put this plot into a variable GA in order to try to use scale_x to format the date:
GA + scale_x_date(labels = date_format("%m/%d"))
But I keep getting this Error:
Error in structure(list(call = match.call(), aesthetics = aesthetics, :
could not find function "date_format"
And if I run this code:
GA + scale_x_date()
I get this error:
Error: Invalid input: date_trans works with objects of class Date only
I am using a Mac OS X running R 2.15.2
Please help.

Answer 1

Its because, df$Month, (assuming your data.frame is df), which is a factor has its levels in this order.
> levels(df$Month)
# [1] "1/1/12" "12/1/12" "4/1/12" "8/1/12"
The solution is to re-order the levels of your factor.
df$Month <- factor(df$Month, levels=df$Month[!duplicated(df$Month)])
> levels(df$Month)
# [1] "1/1/12" "4/1/12" "8/1/12" "12/1/12"
Edit: Alternate solution using strptime
# You could convert Month first:
df$Month <- strptime(df$Month, '%m/%d/%y')
Then your code should work. Check the plot below: