Problems with statistics

Hello,

I have the following csv file

n,	n_red
1,	0
1,	1
2,	1
2,	1
3,	0
4,	1
4,	2
4,	3

I would like to plot this data. On the x-axis there should be n and on  
the y-axis the mean of all n_red where n is the according value on the  
x-axis. The plot should look like plotting the following data:

n,	n_red
1,	0.5
2,	1
3,	0
4,	2

Is there any simple way to do this?

Greetings
odif