Setting conditions in arrays in SAS - arrays

Question

I have a set of data that looks like this:
ID Status31Jan2007 Status28Jan2007 Status31Mar2007
001 0 0
002 1 0 0
003 1 1 0
I have Statusddmmyyyy fields of either '0' or '1' for 118 months. (here, I only have three months as a sample)
I want to get results like this:
ID Flag1 Flag2 Flag3
001 N N N
002 Y N N
003 Y Y N
The logic is, if as at Status31Jan2007 = 1 and the following two months, count of Status fields with 0 > 0, then flag it as 'Y'. Else, N.
Meaning,
If my ID is 001 and as at Status31Jan2007, value is missing, i flag it as 'N' under Flag1.
Moving on to the next month, Status28Feb2007, value is 0, i automatically flag it as 'N' as well under Flag2. This applies to the next month.
Looking at ID 002, Status31Jan2007 is 1. And following two months, I have two 0 values. Count of '0' value is > 0. So I flag it as 'Y' under Flag1.
But as at Status28Feb2007, it is 0. It doesnt fit the criteria so i flag it as 'N' under Flag2.
As long as as at the field, I need the status to be 1 then only I proceed to look into the following two months.
After getting the results, how do I count the number of flags N and Y under each fields?
Count1 Count2 Count3
N 1 2 3
Y 2 1 0
Would appreciate the help as I am new to SAS. Thanks.

Answer 1

This will only work if the column names across are in calendar order.
Use an ARRAY statement to organize and then access variables by index and thus easily process the [index+1] and [index+2] checks your logic indicates. You can also use temporary arrays to maintain a count as you assign the flag values; at the last row the counts are output to a separate table.
Note: for status variables taking on either 0 or 1 the count of 1's can be computed using SUM. The sum of two status variables will be < 2 when either of them is 0.
* simulate some data;
data prelim;
do id = 1 to 20;
do date = '01jan07'd by 1 until(intck('month', '01jan07'd, date) >= 117);
date = intnx('month', date, 1) - 1;
status = ranuni(123) < 0.45;
if date = '31jan07'd and mod(id,5) = 1 then status = .;
output;
end;
end;
format date date9.;
run;
* change the shape of simulated data to match the question;
proc transpose data=prelim prefix=Status out=have(drop=_name_);
by id;
var status;
id date;
run;
* process the problem shaped data;
data
want (keep=id status: flag:)
want_count (keep=flag_value count:);
;
set have end=lastid;
retain sentinel1 sentinel2 0;
array status status: sentinel1 sentinel2; * map all the Status* variables to an array named status;
array flag [118] $1 ; * automatically creates 118 new variables flag1 to flag118;
array yfreq [118] _temporary_ (118*0); * temporary arrays initialized to 0;
array nfreq [118] _temporary_ (118*0);
* process each month status, -2 because of the sentinels ;
do i = 1 to dim(status)-2;
* assign flag according to the logic, some cases require a 2-month look ahead;
select;
when ( status(i) = . ) flag(i) = 'N';
when ( status(i) = 0 ) flag(i) = 'N';
when ( status(i) = 1
and sum(status(i+1),status(i+2)) < 2 ) flag(i) = 'Y'; * SUM trick;
otherwise
flag(i) = 'N';
end;
* track frequencies of flags assigned;
if flag(i) = 'N'
then nfreq(i)+1;
else yfreq(i)+1;
end;
output want;
if lastid then do;
* all flags for all ids have been binned for frequency;
* output the freqs to a count data set;
length flag_value $1;
array freq count1-count118;
flag_value = 'N'; do i = 1 to dim(nfreq); freq(i) = nfreq(i); end; output want_count;
flag_value = 'Y'; do i = 1 to dim(yfreq); freq(i) = yfreq(i); end; output want_count;
end;
run;