topic Re: Finding maximum value in a column within a subset/group in SAS Programming

Finding maximum value in a column within a subset/group

neq1337 — Sat, 08 Dec 2012 19:01:28 GMT

Hello,

I have a data similar to the one below, but without the max3_value column. This is the one I would like to find, but I do not know how.

max3_value takes the last 3 values of the value column (within a group of person) and finds the maximum value of them. Of course, if it is the first or the second observation, it outputs a missing value.

For example: max3_value=10 in period 3 for person A is calculated as a max(10,5,3).

I thought of transposing the data with lagged values, but still I do not know how calculate it within groups of person.

I would kindly appreciate any help.

person	period	value	max3_value
A	1	10	.
A	2	5	.
A	3	3	10
A	4	5	5
A	5	2	5
A	6	3	5
A	7	4	4
A	8	14	14
B	1	6	.
B	2	5	.
B	3	1	6
B	4	1	4
B	5	4	4

Re: Finding maximum value in a column within a subset/group

Tom — Sat, 08 Dec 2012 19:54:12 GMT

One way is populate variables with the previous 2 values and keep count of how many obs you have seen for this person.

data want;

set have;

by person ;

lag1=lag1(value);

lag2=lag2(value);

if first.person then cnt=0;

cnt + 1;

if cnt < 3 then max3=.;

else max3 = max(lag1,lag2,value);

run;

Re: Finding maximum value in a column within a subset/group

art297 — Sat, 08 Dec 2012 19:59:36 GMT

Why is it obvious that the first two values will be missing? Do you always want them to be?

Also, why is the next to the last value for person A assigned the value 4? Was that supposed to be 14?

Re: Finding maximum value in a column within a subset/group

neq1337 — Sat, 08 Dec 2012 20:10:47 GMT

You are right, this is not obvious, but that is the way I want them to be (it makes sense in the original dataset).

max3_value=4 is OK, as it is a max(2,3,4).

Re: Finding maximum value in a column within a subset/group

art297 — Sat, 08 Dec 2012 20:27:38 GMT

Tom's suggested code appears to accomplish what you want.

Re: Finding maximum value in a column within a subset/group

Tom — Sat, 08 Dec 2012 20:28:21 GMT

Actually it should be 5 as the max of 5,1,1 is 5.

Re: Finding maximum value in a column within a subset/group

neq1337 — Sat, 08 Dec 2012 20:32:28 GMT

Thank you for prompt response, it works perfectly.

Re: Finding maximum value in a column within a subset/group

art297 — Sat, 08 Dec 2012 23:28:31 GMT

: You are correct about the line you referenced, but I was asking about an earlier line. I had seen the last three assignments and figured that the OP was simply looking at groups of three.

Regardless, your code apparently does precisely what the OP was looking for.