如何将图例添加到ggplot2折线图？

Question

I have a simple dataframe:

> ih
  year    y1    y2
1 2005  4.50  4.92
2 2006  4.89  6.21
3 2007  6.63  6.68
4 2008  4.89  4.60
5 2009 16.56 15.16
6 2010 17.98 17.73
7 2011 25.92 19.85

And I would like to graph a line chart with year on the x-axis and y1 and y2 as two separate lines, both black and with different line types. How can I get a legend that shows that y1 represents "Bob" and y2 represents "Susan"?

Here is my attempt, which produces the following graph (without a legend):

ggplot(ih, aes(x = year)) + geom_line(aes(y=y1), linetype="dashed") + 
  geom_line(aes(y=y2)) + 
  labs(x="Year", y="Percentage", fill="Data") + 
  geom_point(aes(y=y1)) + 
  geom_point(aes(y=y2))

Thank you for any help! Today is my first day using R!

Answer 1

You should convert your data to long format for example with function melt() from library reshape2 and then use variable to define linetype= in aes() . So legend will be made automatically. To remove name variable in legend you can add scale_linetype("") .

library(reshape2)
ih.long<-melt(ih, id.vars="year")

ih.long
   year variable value
1  2005       y1  4.50
2  2006       y1  4.89
3  2007       y1  6.63
4  2008       y1  4.89
5  2009       y1 16.56
6  2010       y1 17.98
....

ggplot(ih.long,aes(year,value,linetype=variable))+geom_line()+geom_point()+
    scale_linetype("")