topic Why duplicate rows after merging two data sets in SAS Data Management

Why duplicate rows after merging two data sets

sarang — Wed, 04 Mar 2015 08:13:36 GMT

Hello,

I'll truly appreciate if somebody helps me out.

I wonder why I get a data including duplicate rows after merging.

My code is following.

proc sort data=work.A; /**table A has 500 rows**/

by store product week;

proc sort data=work.B; /**table B has 800 rows**/

by store product week;

data work.A;

merge work.A (in=in1) work.B (in=in2 keep=store product week advertise);

by store product week;

if in1;

run;

This code is merging table A and B in order to add "advertise" column in the table A.

I expected the number of table A's rows is 500 since the code has "if in1;". However, it was 800. Does anyone know why?

Jason

Re: Why duplicate rows after merging two data sets

Kurt_Bremser — Wed, 04 Mar 2015 08:54:11 GMT

You get an observation for each matching obs. As long as every obs in work.B has a match in work.A, they will be included in the output set (because the condition if in1 is always met)

If you do not want multiple observations, you need to eliminate the duplicates in Work.B first. Or include a first. or last. condition.

Re: Why duplicate rows after merging two data sets

damanaulakh88 — Wed, 04 Mar 2015 09:37:02 GMT

Hi Sarang,

You need to remove the duplicates using "nodupkey" option while you sort, this would eliminate your issue.

You can try the below code example:

data one;
input store $ product $ week;
cards;
1 a 23
2 b 45
3 a 21
1 a 34
1 a 23
2 b 45
;
run;

data two;
input store $ product $ week advertise $;
cards;
1 a 23 y
2 b 45 y
1 a 34 n
2 b 45 y
3 a 21 y
5 c 45 y
7 d 76 y
;
run;

proc sort data=one nodupkey;
by store product week;
run;

proc sort data=two nodupkey;
by store product week;
run;

data final;
merge one(in=a) two(in=b keep=store product week advertise);
by store product week;
if a;
run;

Output:

Hope this helps!!

Thanks,

Daman

Re: Why duplicate rows after merging two data sets

TomKari — Wed, 04 Mar 2015 15:21:55 GMT

Run this, and take a look at the results. I think this will clarify how the MERGE works.

data a;

input week;

cards;

run;

data b;

input week advertise;

cards;

1 9

2 9

3 9

4 9

run;

data c;

merge a(in=in1) b;

by week;

if in1;

run;

Re: Why duplicate rows after merging two data sets

sarang — Wed, 04 Mar 2015 16:15:17 GMT

I really appreciate your answers!

They clarified my misunderstanding of merging.