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Finding maximum value in a column within a subset/group

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Occasional Contributor
Posts: 5
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Finding maximum value in a column within a subset/group

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.

personperiodvaluemax3_value
A110.
A25.
A3310
A455
A525
A635
A744
A81414
B16.
B25.
B316
B414
B544

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‎12-08-2012 02:54 PM
Super User
Super User
Posts: 7,042

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

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;

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Solution
‎12-08-2012 02:54 PM
Super User
Super User
Posts: 7,042

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

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;

Occasional Contributor
Posts: 5

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

Thank you for prompt response, it works perfectly. Smiley Happy

PROC Star
Posts: 7,471

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

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?

Occasional Contributor
Posts: 5

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

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).

PROC Star
Posts: 7,471

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

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

Super User
Super User
Posts: 7,042

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

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

PROC Star
Posts: 7,471

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

: 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.

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