Creating new variable assigned as an existing variable by conditions

[ldavis020]

Hello! I'm attempting to create a new variable that assigns the mean in period 2 to period 1 for each group. Better to explain with the data. 

This is what I have: 

data have;
input group period mean;
datalines;
1 1 10
1 2 20
2 1 33
2 2 22
3 1 21
3 2 34
4 1 33
4 2 32
;
run;

This is what I want:

data want;
input group period mean meanp2;
datalines;
1 1 10 20 
1 2 20 20
2 1 33 22
2 2 22 22
3 1 21 34
3 2 34 34
4 1 33 32
4 2 32 32
;
run;

[ldavis020 · Accepted solution]

Answered my own question. Sorry thanks!! 

For references the solution is: 

data p2; set have;
meanp2=mean;
where period=2;
run;

data want; 
merge p2 have;
by group;
run;