Create a binary variable from duplicate values

[Alireza_Boloori]

Hello everyone,

Thanks in advance for your help!

I have a data like this:

X1     X2      X3    ...

1       ...        ...

1       ...        ...

2       ...        ...

2       ...        ...

2       ...        ...

3       ...        ...

4       ...        ...

4       ...        ...

and I want to create a new variable (called Y) with binary values, which makes the data as such:

X1     X2      X3    ...  Y

1       ...        ...          0 

1       ...        ...          1

2       ...        ...          0

2       ...        ...          1

2       ...        ...          1

3       ...        ...          0

4       ...        ...          0

4       ...        ...          1

In other words, it puts 0 for a unique value of X1, 0 for the first non-unique value, and 1 for the remainder of non-unique values. I was wondering how it can be done in SAS. Any idea/help is really appreciated!

[Shmuel · Accepted solution]

Assuming data is sorted by X1 then do:

data want;
 set have;
  by X1;
       if first.x1  then y=0; else y=1;
run;

[Alireza_Boloori]

@Shmuel Thank you for the answer!

[Reeza]

Similar method, slightly different calculation, since that's exactly what FIRST does, flip the indicator.

data want;
 set have;
  by X1;

 y=1-first.x1;
run;

[Alireza_Boloori]

@Reeza Thanks!