## selecting a specific sequence of a variable

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Super Contributor
Posts: 459

# selecting a specific sequence of a variable

Hi,

I have the following data:

```data have;
input number sequence @@;
datalines;
1 1 2 1 3 1 4 2 5 1 6 2
7 1 8 1 9 3 10 1
;
run;```

What I would like to obtain are the observations for which the sequence =1 and the sequence of the number right after it is greater than 1:

 number sequence 3 1 4 2 5 1 6 2 8 1 9 3

I was trying to solve this problem with a temporary array that serves as a rolling window:

``````data want;
set have;
array seq [2] _temporary_;

seq [*] = sequence;
if seq[2] > 1 and seq[1] = 1;
run;``````

But was getting an error for the part "seq[*] = sequence" that "Expecting an arihmetic expression"

Thank you!

Accepted Solutions
Solution
‎04-08-2017 08:41 PM
Super User
Posts: 8,213

## Re: selecting a specific sequence of a variable

One way to solve it is by using the lag function. e.g.:

```data want (keep=out: rename=(out_sequence=sequence out_number=number));
set have;
last_sequence=lag(sequence);
last_number=lag(number);
if last_sequence eq 1 and sequence gt 1 then do;
out_sequence=last_sequence;
out_number=last_number;
output;
out_sequence=sequence;
out_number=number;
output;
end;
run;
```

Art, CEO, AnalystFinder.com

All Replies
Solution
‎04-08-2017 08:41 PM
Super User
Posts: 8,213

## Re: selecting a specific sequence of a variable

One way to solve it is by using the lag function. e.g.:

```data want (keep=out: rename=(out_sequence=sequence out_number=number));
set have;
last_sequence=lag(sequence);
last_number=lag(number);
if last_sequence eq 1 and sequence gt 1 then do;
out_sequence=last_sequence;
out_number=last_number;
output;
out_sequence=sequence;
out_number=number;
output;
end;
run;
```

Art, CEO, AnalystFinder.com

Super User
Posts: 8,213

## Re: selecting a specific sequence of a variable

And here is another way to obtain the same result .. although I think using my first suggestion would be slightly faster:

```data want (drop=_:);
merge have have(firstobs=2 keep=sequence rename=(sequence=_sequence));
retain _next;
if sequence eq 1 and _sequence gt 1 then do;
output;
_next=1;
end;
else if _next then do;
output;
_next=0;
end;
run;
```

Art, CEO, AnalystFinder.com

Super User
Posts: 2,037

## Re: selecting a specific sequence of a variable

[ Edited ]

Hi,

data want(drop=flag);
do  until (last.sequence);
set have end=last;
by sequence notsorted;
retain flag;
if last.sequence and sequence=1 and not last then do;
output;
flag=1;
end;
else if first.sequence and flag then do;
output;
flag=0;
end;
end;
run;

Regards,

Naveen Srinivasan

☑ This topic is solved.