CODEWITHSUNDEEP
loopssasgrouping
DukeLuke
DukeLuke

Reputation: 315

SAS -- By-Group Processing Retain with First and Last Dot

I always find myself having to quickly refresh by-group processing when I'm using first dot and last dot variables with data, but today I saw something interesting.

Here's a sample dataset:

data DS1;
input ID1 ID2;
datalines;
1 100
1 200
1 300
2 400
3 500
3 500
4 600
;
run;

I generally use retain with by-group processing and either first or last dot variables to manipulate my data like so:

data ByGroup1;
set DS1;
by ID1 ID2;

retain Count;

if first.ID1 then Count = 0;
Count + 1;

run;

But, I was reading a post of SAS.com where an invidual used the following method (without a retain statement).

data ByGroup2;
set DS1;
by ID1 ID2;

if first.ID1 then Count = 0;
Count + 1;

run;

Both methods return the same dataset:

ID1 ID2 Count
1   100 1
1   200 2
1   300 3
2   400 1
3   500 1
3   500 2
4   600 1

Are variables implicitly retained in the PDV when doing by group processing? Or, is it that the program never returns to the top of the data-step until it reaches the end of the by-group?

I think I'm confused on the mechanics of how this variable is iterating without a retain since I'm so used to explicitly using retain when it's required.

Upvotes: 2

Views: 466

Answers (1)

Tom
Tom

Reputation: 51581

When you use a sum statement the variable is automatically retained. And unless you have defined a different initial value it will be initialized to zero.

The syntax for a sum statement is:

variable + expression ;

Upvotes: 4

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