Keep first date of each month

[NguyenHa]

Dear all,

I have data that I want to keep the first date of every month for every PERMNO. I donot think intnx can do this because all date in one month will change into first date of month, I did try first.date (month, year) but the table still one have 1 observation for 1 permno. 

So could you help me with this? Thanks.  

PERMNO	end	sum	month	year
10006	2/01/1926	0.02055	1	1926	keep
10006	4/01/1926	0.007088	1
10006	5/01/1926	-0.01259	1
10006		…	1
10006	30/01/1926	-0.02597	1
10006	1/02/1926	-0.02574	2		keep
10006	2/02/1926	-0.01599	2
10006			…
10006	1/03/1926	0.111675	3		keep
10006	2/03/1926	0.113096	3
10006			….
10006			12
10006	3/01/1927	0.15162	1	1927	keep
10006	4/01/1927	0.161668
10006	5/01/1927	0.159616
88888	2/01/1926	0.02055	1	1926	keep
88888	4/01/1926	0.007088	1
88888	5/01/1926	-0.01259	1
88888		…	…
88888
88888	1/02/1926	-0.02574	2		keep
88888	2/02/1926	-0.01599	2
88888			…
88888	1/03/1926	0.111675	3		keep
88888	2/03/1926	0.113096	3

[Reeza]

Sort appropriately and use FIRST. 

data want;

set have;

by permno year month;

if first.month;

run;

[PeterClemmensen · Accepted solution]

data have;
input PERMNO end :ddmmyy10.  sum;
format end ddmmyy10.;
month = month(end);year = year(end);
datalines;
10006	2/01/1926	0.02055	
10006	4/01/1926	0.007088
10006	5/01/1926	-0.01259
10006	30/01/1926	-0.02597
10006	1/02/1926	-0.02574
10006	2/02/1926	-0.01599
10006	1/03/1926	0.111675
10006	2/03/1926	0.113096
10006	3/01/1927	0.15162
10006	4/01/1927	0.161668
10006	5/01/1927	0.159616
88888	2/01/1926	0.02055
88888	4/01/1926	0.007088
88888	5/01/1926	-0.01259
88888	1/02/1926	-0.02574
88888	2/02/1926	-0.01599
88888	1/03/1926	0.111675
88888	2/03/1926	0.113096
;

proc sort data = have;
   by permno year month;
run;

data want;
   set have;
   by permno year month;

   if first.month;
run;

[NguyenHa]

Thank you very much, it works.


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