Hi Everyone,
I have a dataset looking like this:

Date id var1 var2 var3 var4...
2010 1 ... ... ... ...
2010 1 ... ... ... ...
2010 1 ... ... ... ...
2010 2 ... ... ... ...
2010 2 ... ... ... ...
2010 2 ... ... ... ...
2010 3 ... ... ... ...
2010 3 ... ... ... ...
2010 3 ... ... ... ...

I'd like to find mean of each variable by id. That is, at the end, I want to achieve something like this:


Date id mean_var1 mean_var2 mean_var3 mean_var4...
2010 1 ... ... ... ...
2010 2 ... ... ... ...
2010 3 ... ... ... ...

It would be great if you can help. Thank you in advance.
Best,