Comparison of variable length definition methods

This script presents three approaches to creating a conditional variable 'result' in a Data step. It illustrates how SAS^© determines the length of a character variable: implicitly via the first assignment (causing potential truncation), implicitly via a string of spaces, or explicitly via the LENGTH statement (best practice). It also calculates averages via the MEAN function and an arithmetic formula to show the different handling of missing values.

Data Analysis

Type : INTERNAL_CREATION

Data is generated directly in the code using the DATALINES statement.

1 Code Block

DATA STEP Data

Explanation :
Creation of the Grades1 table. WARNING: The 'result' variable is initialized to '' (empty string), which sets its length to 1 character. The values 'Failed' and 'Passed' will be truncated to 'F' and 'P'.

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1	DATA Grades1;
2	INPUT subj 1-4 name $ 5-23 sex exam1 exam2 exam3 exam4 exam5 project finalexam;
3	actualavg = mean(exam1,exam2,exam3,exam4,exam5,project,finalexam);
4	avgscore = (exam1+exam2+exam3+exam4+exam5+project+finalexam)/7;
5
6	IF avgscore=. THEN RESULT=''; * missing value;
7	ELSE IF avgscore < 80 THEN RESULT='Failed';
8	ELSE RESULT='Passed';
9	DATALINES;
10	1011 Alia Bhatt 2 100 65 83 84 99 91 96
11	1012 Maria Smith 1 78 82 86 . 100 95 97
12	1111 Thomas Jones 2 88 81 96 69 91 90 98
13	1121 Benedictine Arnold 2 68 82 82 89 89 93 99
14	1301 Trisha Gupta 1 51 69 79 59 85 64 100
15	;
16	RUN;

2 Code Block

PROC PRINT

Explanation :
Display of Grades1 to observe the truncation of the 'result' variable.

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1
2	PROC PRINT
3	DATA=Grades1;
4	var name avgscore actualavg RESULT;
5	RUN;
6

3 Code Block

DATA STEP Data

Explanation :
Creation of Grades2. Here, 'result' is initialized with a 9-space string. This implicitly forces the length to 9, avoiding truncation, but consumes unnecessary space if the string is empty.

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1	DATA Grades2;
2	INPUT subj 1-4 name $ 5-23 sex exam1 exam2 exam3 exam4 exam5 project finalexam;
3	actualavg = mean(exam1,exam2,exam3,exam4,exam5,project,finalexam);
4	avgscore = (exam1+exam2+exam3+exam4+exam5+project+finalexam)/7;
5
6	IF avgscore=. THEN RESULT=' '; * missing value;
7	ELSE IF avgscore < 80 THEN RESULT='Failed';
8	ELSE RESULT='Passed';
9	DATALINES;
10	1011 Alia Bhatt 2 100 65 83 84 99 91 96
11	1012 Maria Smith 1 78 82 86 . 100 95 97
12	1111 Thomas Jones 2 88 81 96 69 91 90 98
13	1121 Benedictine Arnold 2 68 82 82 89 89 93 99
14	1301 Trisha Gupta 1 51 69 79 59 85 64 100
15	;
16	RUN;

4 Code Block

PROC PRINT

Explanation :
Display of Grades2. The values 'Failed' and 'Passed' appear correctly.

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1
2	PROC PRINT
3	DATA=Grades2;
4	var name avgscore actualavg RESULT;
5	RUN;
6

5 Code Block

DATA STEP Data

Explanation :
Creation of Grades3. Using the 'LENGTH result $8.;' statement before using the variable. This is the recommended method for precisely controlling the type and length of variables.

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1	DATA Grades3;
2	LENGTH RESULT $8.;
3	INPUT subj 1-4 name $ 5-23 sex exam1 exam2 exam3 exam4 exam5 project finalexam;
4	actualavg = mean(exam1,exam2,exam3,exam4,exam5,project,finalexam);
5	avgscore = (exam1+exam2+exam3+exam4+exam5+project+finalexam)/7;
6
7	IF avgscore=. THEN RESULT=''; * missing value;
8	ELSE IF avgscore < 80 THEN RESULT='Failed';
9	ELSE RESULT='Passed';
10	DATALINES;
11	1011 Alia Bhatt 2 100 65 83 84 99 91 96
12	1012 Maria Smith 1 78 82 86 . 100 95 97
13	1111 Thomas Jones 2 88 81 96 69 91 90 98
14	1121 Benedictine Arnold 2 68 82 82 89 89 93 99
15	1301 Trisha Gupta 1 51 69 79 59 85 64 100
16	;
17	RUN;

6 Code Block

PROC PRINT

Explanation :
Final display of Grades3 confirming correct variable handling.

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1
2	PROC PRINT
3	DATA=Grades3;
4	var name avgscore actualavg RESULT;
5	RUN;
6

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