topic Re: Correct use of the "first." statement in SAS Programming

Correct use of the "first." statement

Foodscience_76 — Tue, 05 Feb 2013 14:39:47 GMT

Hi! I am working on a sas code including a loop to make a sum of food intakes. Every subject has an ID and for each ID I have different strings, one for each food item consumed during the day. The goal is to obtain the total amount eaten every day by each subject, i.e.: the sum of each food variable for every ID.

Here is the program I am using, which seems correct to me, but SAS keep saying that the variable first.id_no is not initialized:

data dataset; set dataset;

if first.id_no then do; sum0 = 0; sum1 = 0; sum2 = 0; sum3 = 0; end;

sum0 = sum0 + intake*(vegetables = 1);

sum1 = sum1 + intake*(fruit = 1);

sum2 = sum2 + intake*(cereals = 1);

sum3 = sum3 + intake*(fish = 1);

run;

Alternatively I have tried to write:

if (first.id_no) then do;

if first.id_no = 1 then do;

always getting the same error message from SAS.

Thanks for your help!

Re: Correct use of the "first." statement

LinusH — Tue, 05 Feb 2013 15:02:15 GMT

I'm not sure about your code is doing what you want, but to make use of first. you must declare the column in a BY statement.

Re: Correct use of the "first." statement

happyuser — Tue, 05 Feb 2013 15:29:36 GMT

I often make this mistake. I have to go back and do a PROC SORT using the variable in the BY statement.

Re: Correct use of the "first." statement

OS2Rules — Tue, 05 Feb 2013 15:37:01 GMT

In order to user the "first" and "last" you need to sort your data by the variable (in your case - id_no).

Proc sort data=dataset;

by id_no;

run;

data have;

set dataset

by id_no;

if first.id_no then ...etc....

Re: Correct use of the "first." statement

data_null__ — Tue, 05 Feb 2013 16:02:15 GMT

Foodscience_76 wrote:

The goal is to obtain the total amount eaten every day by each subject, i.e.: the sum of each food variable for every ID.

If this is your goal you will be better off using a procedure like MEANS/SUMMARY.

Re: Correct use of the "first." statement

Foodscience_76 — Tue, 05 Feb 2013 16:05:01 GMT

Thank you everybody for your help! It was in fact very simple, just sorting and adding a BY statement.