SAS for following scenario (most frequent observation) - sas

Question

Assume I have a data-set D1 as follows:
ID ATR1 ATR2 ATR3
1 A R W
2 B T X
1 A S Y
2 C T E
3 D U I
1 T R W
2 C X X
I want to create a data-set D2 from this as follows
ID ATR1 ATR2 ATR3
1 A R W
2 C T X
3 D U I
In other words, Data-set D2 consists of unique IDs from D1. For each ID in D2, the values of ATR1-ATR3 are selected as the most frequent (of the respective variable) among the records in D1 with the same ID. For example ID = 1 in D2 has ATR1 = A (most frequent).
I have one solution which is very clumsy. I simply sort copies of the data set `D1' three times (by ID and ATR1 e.g) and remove duplicates. I later merge the three data-sets to get what I want. However, I think there might be an elegant way to do this. I have about 20 such variables in the original data-set.
Thanks

Answer 1

/*
read and restructure so we end up with:
id attr_id value
1 1 A
1 2 R
1 3 W
etc.
*/
data a(keep=id attr_id value);
length value $1;
array attrs_{*} $ 1 attr_1 - attr_3;
infile cards;
input id attr_1 - attr_3;
do attr_id=1 to dim(attrs_);
value = attrs_{attr_id};
output;
end;
cards;
1 A R W
2 B T X
1 A S Y
2 C T E
3 D U I
1 T R W
2 C X X
;
run;
/* calculate frequencies of values per id and attr_id */
proc freq data=a noprint;
tables id*attr_id*value / out=freqs(keep=id attr_id value count);
run;
/* sort so the most frequent value per id and attr_id ends up at the bottom of the group.
if there are ties then it's a matter of luck which value we get */
proc sort data = freqs;
by id attr_id count;
run;
/* read and recreate the original structure. */
data b(keep=id attr_1 - attr_3);
retain attr_1 - attr_3;
array attrs_{*} $ 1 attr_1 - attr_3;
set freqs;
by id attr_id;
if first.id then do;
do i=1 to dim(attrs_);
attrs_{i} = ' ';
end;
end;
if last.attr_id then do;
attrs_{attr_id} = value;
end;
if last.id then do;
output;
end;
run;