Issues Regarding SAS - arrays

Question

I was working on a homework problem regarding using arrays and looping to create a new variable to identify the date of when the maximum blood lead value was obtained but got stuck. For context, here is the homework problem:
In 1990 a study was done on the blood lead levels of children in Boston. The following variables for twenty-five children from the study have been entered on multiple lines per subject in the file lead_sum2018.txt in a list format:
Line 1
ID Number (numeric, values 1-25)
Date of Birth (mmddyy8. format)
Day of Blood Sample 1 (numeric, initial possible range: -9 to 31)
Month of Blood Sample 1 (numeric, initial possible range: -9 to 12)
Line 2
ID Number (numeric, values 1-25)
Day of Blood Sample 2 (numeric, initial possible range: -9 to 31)
Month of Blood Sample 2 (numeric, initial possible range: -9 to 12)
Line 3
ID Number (numeric, values 1-25)
Day of Blood Sample 3 (numeric, initial possible range: -9 to 31)
Month of Blood Sample 3 (numeric, initial possible range: -9 to 12)
Line 4
ID Number (numeric, values 1-25)
Blood Lead Level Sample 1 (numeric, possible range: 0.01 – 20.00)
Blood Lead Level Sample 2 (numeric, possible range: 0.01 – 20.00)
Blood Lead Level Sample 3 (numeric, possible range: 0.01 – 20.00)
Sex (character, ‘M’ or ‘F’)
All blood samples were drawn in 1990. However, during data entry the order of blood samples was scrambled so that the first blood sample in the data file (blood sample 1) may not correspond to the first blood sample taken on a subject, it could be the first, second or third. In addition, some of the months and days and days of blood sampling were not written on the forms. At data entry, missing month and missing day values were each coded as -9.
The team of investigators for this project has made the following decisions regarding the missing values. Any missing days are to set equal to 15, any missing months are to be set equal to 6. Any analyses that are done on this data set need to follow those decisions. Be sure to implement the SAS syntax as indicated for each question. For example, use SAS arrays and loops if the item states that these must be used.
Here is the data that the HW references (it is in list format and was contained in a separate file called lead_sum2018.txt):
1 04/30/78 6 10
1 -9 7
1 14 1
1 1.62 1.35 1.47 F
2 05/19/79 27 11
2 20 -9
2 5 6
2 1.71 1.31 1.76 F
3 01/03/80 11 7
3 6 6
3 27 2
3 3.24 3.4 3.83 M
4 08/01/80 5 12
4 28 -9
4 3 4
4 3.1 3.69 3.27 M
5 12/26/80 21 5
5 3 7
5 -9 12
5 4.35 4.79 5.14 M
6 06/20/81 7 10
6 11 3
6 22 1
6 1.24 1.16 0.71 F
7 06/22/81 19 6
7 3 12
7 29 8
7 3.1 3.21 3.58 F
8 05/24/82 26 7
8 31 1
8 9 10
8 2.99 2.37 2.4 M
9 10/11/82 2 7
9 25 5
9 28 3
9 2.4 1.96 2.71 F
10 . 10 8
10 30 12
10 28 2
10 2.72 2.87 1.97 F
11 11/16/83 19 4
11 15 11
11 7 -9
11 4.8 4.5 4.96 M
12 03/02/84 17 6
12 11 2
12 17 11
12 2.38 2.6 2.88 F
13 04/19/84 2 12
13 -9 6
13 1 7
13 1.99 1.20 1.21 M
14 02/07/85 4 5
14 17 5
14 21 11
14 1.61 1.93 2.32 F
15 07/06/85 5 2
15 16 1
15 14 6
15 3.93 4 4.08 M
16 09/10/85 12 10
16 11 -9
16 23 6
16 3.29 2.88 2.97 M
17 11/05/85 12 7
17 18 1
17 11 11
17 1.31 0.98 1.04 F
18 12/07/85 16 2
18 18 4
18 -9 6
18 2.56 2.78 2.88 M
19 03/02/86 19 4
19 11 3
19 19 2
19 0.79 0.68 0.72 M
20 08/19/86 21 5
20 15 12
20 -9 4
20 0.66 1.15 1.42 F
21 02/22/87 16 12
21 17 9
21 13 4
21 2.92 3.27 3.23 M
22 10/11/87 7 6
22 1 12
22 -9 3
22 1.43 1.42 1.78 F
23 05/12/88 12 2
23 21 4
23 17 12
23 0.55 0.89 1.38 M
24 08/07/88 17 6
24 27 11
24 6 2
24 0.31 0.42 0.15 F
25 01/12/89 4 7
25 15 -9
25 23 1
25 1.69 1.58 1.53 M
A) Input the data and in the data step:
1) make sure that Date of Birth variable is recorded as a SAS date;
2) use SAS arrays and looping to create a SAS date variable for each of the three blood samples and to address the missing data in accordance to the decisions of the investigators. Hint: use a single array and do loop to recode the missing values for day and month, separately, and an array/do loop for creating the SAS date variable;
3) use a SAS function to create a variable for the highest, i.e., maximum, blood lead value for each child;
4) use SAS arrays and looping to identify the date on which this largest value was obtained and create a new variable for the date of the largest blood lead value;
5) determine the age of the child in years when the largest blood lead value was obtained (rounded to two decimal places);
6) create a new variable based on the age of the child in years when the largest lead value was obtained (call it, “agecat”) that takes on three levels: for children less than 4 years old, agecat should equal 1; for children at least 4 years old, but less than 8, agecat should equal 2; and for children at least 8 years of age, agecat should be 3.;
7) print out the variables for the date of birth, date of the largest lead level, age at blood sample for the largest blood lead level, agecat, sex, and the largest blood lead level (Only print out these requested variables). All dates should be formatted to use the mmddyy10. format on the output.
The code I used in response to this was:
libname HW3 'C:\Users\johns\Desktop\SAS';
filename HW3new 'C:\Users\johns\Desktop\SAS\lead_sum2018.txt';
data one;
infile HW3new;
informat dob mmddyy8.;
input #1 id dob dbs1 mbs1
#2 dbs2 mbs2
#3 dbs3 mbs3
#4 bls1 bls2 bls3 sex;
array dbs{3} dbs1 dbs2 dbs3;
array mbs{3} mbs1 mbs2 mbs3;
do i=1 to 3;
if dbs{i}=-9 then dbs{i}=15;
end;
do i=4 to 6;
if mbs{i}=-9 then mbs{i}=6;
end;
array date{3} mdy1 mdy2 mdy3;
do i=1 to 3;
date{i}=mdy(mbs{i}, dbs{i}, 1990);
end;
maxbls=max(of bls1-bls3);
array bls{3} bls1 bls2 bls3;
array maxdte{3} maxdte1 maxdte2 maxdte3;
do i=1 to i=3;
if bls{i}=maxbls then maxdte=i;
end;
agemax=maxdte-dob;
ageest=round(agemax/365.25,2);
if agemax=. then agecat=.;
else if agemax < 4 then agecat=1;
else if 4 <= agemax < 8 then agecat=2;
else if agemax ge 8 then agecat=3;
run;
I received this error:
22 maxbls=max(of bls1-bls3);
23 array bls{3} bls1 bls2 bls3;
24 array maxdte{3} maxdte1 maxdte2 maxdte3;
25 do i=1 to i=3;
26 if bls{i}=maxbls then maxdte=i;
ERROR: Illegal reference to the array maxdte.
27 end;
Does anyone have any tip is regards to this issue? What did I do wrong? Was I supposed to create an additional array for the date of when the maximum blood lead sample value was collected? Thanks!
**I'm stuck on #4 of Part A, but I included the other parts for context. Thanks!
**Edits: I included the data that I had to read into SAS and the file name of the file it came from

Answer 1

Just from looking at the code immediately prior to the error, you have a problem on this line:
26 if bls{i}=maxbls then maxdte=i;
You are getting the error because you are attempting to assign a value to the array maxdte. Arrays cannot be assigned values like that (unless you are using the deprecated do over syntax...) Instead, choose an element of the array and assign the value to the element. E.g. you could do:
26 if bls{i}=maxbls then maxdte{1}=i;
Or instead of a literal 1, you could use a variable containing the relevant array index.

Answer 2

You are not properly handling ID field from lines #2-4
input #1 id dob dbs1 mbs1
#2 dbs2 mbs2
#3 dbs3 mbs3
#4 bls1 bls2 bls3 sex;
For example you need to skip field 1 on line 2-3 or read the ids into array perhaps to check they are all the same.
input #1 id dob dbs1 mbs1
#2 id2 dbs2 mbs2
#3 id3 dbs3 mbs3
#4 id4 bls1 bls2 bls3 sex;
This example show how to check that you have 4 lines with the same ID and if you do read the rest of the variables or execute LOSTCARD. ID 3 has a missing record;
353 data ex;
354 infile cards n=4 stopover;
355 input #1 id #2 id2 #3 id3 #4 id4 #;
356 if id eq id2 eq id3 eq id4
357 then input #1 id dob:mmddyy. dbs1 mbs1
358 #2 id2 dbs2 mbs2
359 #3 id3 dbs3 mbs3
360 #4 id4 bls1 bls2 bls3 sex :$1.;
361 else lostcard;
362 format dob mmddyy.;
363 cards;
NOTE: LOST CARD.
RULE: ----+----1----+----2----+----3----+----4----+----5----+----6----+----7----+----8----+----9----+----0
372 3 01/03/80 11 7
373 3 27 2
374 3 3.24 3.4 3.83 M
375 4 08/01/80 5 12
NOTE: LOST CARD.
376 4 28 -9
NOTE: LOST CARD.
377 4 3 4
NOTE: The data set WORK.EX has 3 observations and 15 variables.
data ex;
infile cards n=4 stopover;
input #1 id #2 id2 #3 id3 #4 id4 #;
if id eq id2 eq id3 eq id4
then input #1 id dob:mmddyy. dbs1 mbs1
#2 id2 dbs2 mbs2
#3 id3 dbs3 mbs3
#4 id4 bls1 bls2 bls3 sex :$1.;
else lostcard;
format dob mmddyy.;
cards;
1 04/30/78 6 10
1 -9 7
1 14 1
1 1.62 1.35 1.47 F
2 05/19/79 27 11
2 20 -9
2 5 6
2 1.71 1.31 1.76 F
3 01/03/80 11 7
3 27 2
3 3.24 3.4 3.83 M
4 08/01/80 5 12
4 28 -9
4 3 4
4 3.1 3.69 3.27 M
;;;;
run;
proc print;
run;