Help using Base SAS procedures

How to use lag function recursively

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Contributor
Posts: 33
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How to use lag function recursively

Hi,

I have a huge data with a lot of missing values for a variable.  For example,

Data a;

     input x y;

     cards;

1 1

1 0

1 .

1 .

2 2

2 3

2 9

2 .

2 .

;

run;

Now I want to fill in the missing y with its lagged value. That is, for x=1, y=0 for the missing ones and x=2, y=9 for the last two observations. But when I use lag function, it only fills in the first missing observation.

Can anyone please tell me how to do this? Please note, the data is large. So it's better to avoid open/close data too many times.

Thanks,

Sunny


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‎11-13-2014 10:50 PM
Trusted Advisor
Posts: 1,228

Re: How to use lag function recursively

Posted in reply to Sunny_Sun

data want(drop=y rename=(y1=y));

set a;

retain y1;

if y>. then y1=y;

run;

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Respected Advisor
Posts: 4,923

Re: How to use lag function recursively

Posted in reply to Sunny_Sun

It is probably simpler than you thought with UPDATE processing:

data want;

update a(obs=0) a;

by x;

output;

run;

PG

PG
Solution
‎11-13-2014 10:50 PM
Trusted Advisor
Posts: 1,228

Re: How to use lag function recursively

Posted in reply to Sunny_Sun

data want(drop=y rename=(y1=y));

set a;

retain y1;

if y>. then y1=y;

run;

Trusted Advisor
Posts: 3,214

Re: How to use lag function recursively

Posted in reply to Sunny_Sun

The lag function in SAS is a queue functionality and is quite different then the lag en lead functions in Oracle / MS-Sql

For not getting confused avoid using that same name for that.

What you are possible trying to do is known as "impute missings"  as that is part of the mining steps.

Just putting in the previous value is not the best strategy to do that, there are several more approaches .

---->-- ja karman --<-----
Contributor
Posts: 33

Re: How to use lag function recursively

Posted in reply to Sunny_Sun

Many thanks all of you!

Thanks,

Sunny

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