Working with maximum values in SAS - count

Question

Hopefully a straight forward answer, but how can I determine if a variable has more then one observation that equals the maximum? For example, if the following is my data:
ID Doctor COUNT
576434 Tim 1
576434 Lynn 1
576434 Moran 1
576434 Wade 2
576434 Ashwin 2
Looking at the variable "COUNT", we can see that two observations equal the maximum value 2. I would then want to flag this "ID" as having a tie. The data is already in order by ID then COUNT, so my thought was maybe to just see if the values in the last two rows equal, but hoping for a better way. Thanks!

Answer 1

Ok, take a look at this strange solution...
First, your data (with a few more lines to test it out)
data have;
format
ID 8.
Doctor $10.
COUNT 8.;
input
#1 ID 8.
#8 Doctor $7.
#16 COUNT 8.;
DATALINES;
576434 Tim 1
576434 Lynn 1
576434 Moran 1
576434 Wade 2
576434 Ashwin 2
111111 AAAAAA 1
111111 BBBBBB 2
111111 CCCCCC 3
111111 DDDDDD 3
111111 EEEEEE 3
222222 ZZZZZZ 1
222222 WWWWWW 2
;
RUN;
proc sort data=have;
by ID;
run;
Create a dataset to help us, selecting only those max values which count > 1 by ID
proc sql;
CREATE TABLE AUX AS
SELECT
ID
,MAX(COUNT) AS AUXCOUNT
FROM (
SELECT
ID
,COUNT
,COUNT(*) AS COUNTOBS
FROM HAVE
GROUP BY 1,2
HAVING CALCULATED COUNTOBS > 1
)
GROUP BY 1
ORDER BY 1;
quit;
Merge with the first data set to flag the data when there's a tie:
data want;
merge
have (in=a)
aux (in=b);
by ID;
if count = auxcount then TIEFLAG = "TIE";
else TIEFLAG = "";
drop auxcount;
run;
RESULT
ID DOCTOR COUNT FLAG
111111 AAAAAA 1
111111 BBBBBB 2
111111 CCCCCC 3 TIE
111111 DDDDDD 3 TIE
111111 EEEEEE 3 TIE
222222 ZZZZZZ 1
222222 WWWWWW 2
576434 Tim 1
576434 Lynn 1
576434 Moran 1
576434 Wade 2 TIE
576434 Ashwin 2 TIE

Answer 2

Let's assume your dataset has additional rows for example's sake:
data have;
input ID Doctor$ Count;
datalines;
576434 Tim 1
576434 Lynn 1
576434 Moran 1
576434 Wade 2
576434 Ashwin 2
576435 Barry 8
576435 Jim 10
576435 Bart 10
576391 Tom 1
576391 Bill 2
run;
Step 1: Sort your dataset by ID, descending Count
proc sort data=have;
by ID descending count;
run;
We now have the original dataset put in an order that we can work with. Next, we we'll remove duplicate max entries.
Step 2: Remove duplicates for ID descending Count
proc sort data=have
out=_temp_
dupout=dupes
nodupkey;
by ID descending count;
run;
We don't care about the output dataset from proc sort, but we do care about the dupout dataset.
Dupes
ID Doctor Count
576434 Ashwin 2 <---- Duplicate max
576434 Lynn 1
576434 Moran 1
576435 Bart 10 <---- Duplicate max
Step 3: Pick out the duplicates
Notice that the start of each ID group is the max duplicate value. Since it's sorted by ID, then count in descending order, the very first entry of each ID group in the dupout dataset will get us every instance of a duplicate max. Because everything is sorted thanks to proc sort, this trick will work without errors.
data dupe_max;
set dupes;
by ID descending count;
if(first.ID);
keep ID;
run;
Step 4: Merge these IDs back with the original sorted dataset
data want;
merge dupes(in=dupmax)
have(in=all);
by ID;
Duplicate_Max = (have=dupes);
run;
Two things are going on here:
The in= option allows us to create a Boolean variable that tells us which dataset the observation is coming from. In other words, if the ID exists in dupes, the variable dupmax = 1. If the ID exists in have, the variable all = 1.
variable = (logic here) is a shorthand way of creating Boolean 1/0 variables. You can get the same result by doing:
if(have=dupes) then Duplicate_Max = 1; else Duplicate_Max = 0;
Behind the scenes, this is what's happening:
ID from have ID from dupes
vvv vvvvvv
ID Doctor Count Duplicate_Max all dupmax Match?
576391 Bill 2 0 1 0 No
576391 Tom 1 0 1 0 No
576434 Wade 2 1 1 1 Yes
576434 Ashwin 2 1 1 1 Yes
576434 Tim 1 1 1 1 Yes
576434 Lynn 1 1 1 1 Yes
576434 Moran 1 1 1 1 Yes
576435 Jim 10 1 1 1 Yes
576435 Bart 10 1 1 1 Yes
576435 Barry 8 1 1 1 Yes

Answer 3

It's simpler to do it in SQL. You don't even need to sort. Assuming your source data set is "have" as either of the two other posters provided:
PROC SQL ;
CREATE TABLE dupemax AS
SELECT a.id, a.count, a.numobs
FROM (SELECT id, count, COUNT(*) AS numobs
FROM have
GROUP BY id, count
) a
%* gives the number of rows with each id/count combination ;
INNER JOIN
(SELECT id, MAX(count) AS count
FROM have
GROUP BY id
) b
%* finds the id/MAX(count) value ;
ON a.id EQ b.id AND a.count EQ b.count
%* so only getting the id and the MAX(count), not all "count" values ;
WHERE a.numobs GE 2
%* and of the id/MAX(count), only where there were multiple rows of the MAX(count) ;
;
QUIT ;