Modifying Aesthetics - ggplot2

Question

I am trying to learn ggplot2 and have made below plots:

Using this code:

library(ggplot2); library(gridExtra)
gg <- ggplot(mydata,aes(x=Level))
plot1 <- gg + geom_line(aes(y=Experience,colour="xp"),size=1) +
    labs(title="xp") 
g <- ggplot(mydata,aes(x=Level))
plot2 <- g + geom_line(aes(y=Experience,colour="xp"),size=1) + geom_line(aes(y=Accu,colour="accu"),size=1) +
    labs(title="xp vs Accumulated") 
grid.arrange(plot1,plot2,ncol=2)

Where mydata is a data frame containing 3 columns ( Level , xp and accu ) and 30 rows.

What I am wondering is:

1. How to get the y-axis on the left-hand plot to have the same form as the right-hand plot.
2. How to make the color of "xp" the same in both plots without removing the descriptions of what the lines represent.

Answer 1

How about this (with some random data)?

library(ggplot2) 
library(gridExtra)
library(scales)

gg <- ggplot(mydata,aes(x=Level))
plot1 <- gg + geom_line(aes(y=Experience,colour="xp"),size=1) +
  labs(title="xp") + scale_y_continuous(labels = comma) +   
  scale_colour_manual(values = c("red"))

g <- ggplot(mydata,aes(x=Level))
plot2 <- g + geom_line(aes(y=Experience,colour="xp"),size=1) + 
   geom_line(aes(y=Accu,colour="accu"),size=1) +
   labs(title="xp vs Accumulated")  + scale_y_continuous(labels = comma) + 
   scale_colour_manual(values = c("blue", "red"))

grid.arrange(plot1,plot2,ncol=2)