Understanding the SUBSTR Function in SAS: A Complete Guide

When working with character data in SAS, extracting parts of strings is a common task. Whether you're cleaning raw data or generating new variables, the SUBSTR function becomes an essential tool in your SAS programming toolbox.

In this blog post, we'll break down what the SUBSTR function does, how it works, and provide real-world examples to help you master its usage.

🔍 What is the SUBSTR Function in SAS?

The SUBSTR function in SAS is used to extract a substring from a character variable or string. You can specify the starting position and the length of the substring you want to extract.

Syntax:

SUBSTR(string, start-position <, length>)

• string: The character string or variable.
• start-position: The starting position (1-based index).
• length (optional): Number of characters to extract. If omitted, the substring continues to the end of the string.

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✅ Key Features of SUBSTR

• It is case-sensitive.
• Can be used both on the left-hand side (LHS) and right-hand side (RHS) of assignment.
• Useful for data cleaning, transformation, and feature engineering.

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🧪 Examples of SUBSTR in Action

Example 1: Extracting a Substring from a Character Variable

data example1;
   name = "JohnDoe";
   first_name = substr(name, 1, 4); /* Extracts 'John' */
run;

Example 2: Using SUBSTR Without Length (Extract till End)

data example2;
   id = "EMP12345";
   emp_code = substr(id, 4); /* Extracts '12345' */
run;

Example 3: Using SUBSTR on the Left Side to Modify a String

data example3;
   phone = "9876543210";
   substr(phone, 1, 3) = "999"; /* Replaces first 3 characters */
run;

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⚠️ Common Pitfalls

• Position starts at 1, not 0 like in some other programming languages.
• If the start-position exceeds the string length, SUBSTR returns a blank.
• If you try to modify a variable using SUBSTR on LHS, ensure the variable has enough allocated length.

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📌 Use Cases in Real-world SAS Programming

• Extracting codes from structured IDs (e.g., EMP001, PROD2023)
• Parsing CSV or fixed-width text fields
• Replacing characters at specific positions
• Creating derived variables for reports and models

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💡 Tips for Using SUBSTR Effectively

• Combine SUBSTR with INDEX, SCAN, or FIND for dynamic substring extraction.
• Always use the LENGTH statement to define the expected length of output variables.
• For numeric values, convert using PUT() before applying SUBSTR.

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🧭 Conclusion

The SUBSTR function is a versatile tool in SAS that enables efficient string manipulation. Mastering it not only simplifies your data processing tasks but also enhances your ability to handle messy or semi-structured data with ease.