SAS Array Counting Guide

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How to use arrays and loops in SAS to count conditional values

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Zane Wubbena

Admin

SAS Program

Overview

Introduction

Schools are assigned annual special education determination levels (DL):

  • DL 1: Meets Requirements
  • DL 2: Needs Assistance
  • DL 3: Needs Intervention
  • DL 4: Needs Substantial Intervention

Data Analysis Problem

We need to count variables in a SAS dataset that have a specific determination level value (in this case, 4). This counting helps with:

  • Data summarization
  • Tracking condition occurrences
  • Reporting and analysis according to OSEP QA 23-01

Solution Approach

The solution uses two key SAS programming elements:

  • An array to group related variables
  • A do loop to automatically check each variable

Instead of manual checking, this automated approach:

  • Examines each variable in the array
  • Counts occurrences of the value 4
  • Stores the final count in a new variable (TOTAL_NSI_CNT)

Understanding the Array and its Components

Let’s break down how this process works in simple steps.

1. Initializing a Variable:

  • Before starting the loop, we initialize a variable that will hold the count of how many variables meet the condition.
  • Initialization means setting a starting value for a variable.
    • In this case, the variable TOTAL_NSI_CNT is initialized to 0. This means it starts at 0 because we haven’t counted anything yet.
  • Example from the code:

TOTAL_NSI_CNT = 0;

  • This ensures that the counter starts fresh for each row of data.

2. Defining an Array

  • Arrays in programming allow us to group multiple variables together and treat them as a single entity. This way, we can apply the same logic to all the variables in the array without writing repetitive code.
  • In the example, the array dv_vars contains seven variables (DL_18, DL_19, DL_20, DL_21, DL_22, DL_23, and DL_24).
  • The array definition looks like this:

array dv_vars[7] DL_18 DL_19 DL_20 DL_21 DL_22 DL_23 DL_24;

  • This creates a list of variables that we want to check for the value 4.

3. Using a Do Loop to Process Each Element

  • A do loop is a programming structure that repeats a set of instructions until a condition is met. Here, we are using the loop to go through each variable in the array and check if it equals 4.
  • The do loop looks like this:

do i = 1 to dim(dv_vars);

  • What does this mean?
    • i is a loop counter that keeps track of which element of the array we are working on.
    • dim(dv_vars) returns the number of elements in the array (which is 7 in this case).
    • The loop starts at 1 (the first element in the array) and goes up to the total number of elements [dim(dv_vars)], which in this case is 7.

4. Checking the Condition

• Inside the loop, the code checks whether each element of the array is equal to 4.
• This is done using the statement:

if dv_vars[i] = 4 then TOTAL_NSI_CNT + 1;

  • dv_vars[i] refers to the current element in the array (e.g., DL_18, … DL_24).
  • If the current element is equal to 4, the counter TOTAL_NSI_CNT is incremented by 1.
  • Incrementing the counter means adding 1 to the current value of the counter. If the counter was at 2, and another variable meets the condition, the counter becomes 3. This mean that three of the seven variables had a value of 4.

4. Dropping the Loop Index Variable

  • Once the loop has finished checking all the elements in the array, the loop index variable i is no longer needed. We drop it from the dataset to avoid unnecessary clutter.
  • This is done using the drop statement:

drop i;

SAS Code Full Example

Here’s how the entire block of SAS code looks when put together:

SAS Program

Color-coded syntax highlighting for:

  • Keywords (blue)
  • Comments (green)
  • Variables (purple)

Key Concepts Recap

  • Initialize a Variable: Setting a starting value for a variable before using it. In this case, we initialize TOTAL_NSI_CNT = 0 to start counting from zero.
  • Array: A collection of variables treated as a group. In this case, the array dv_vars holds the variables we want to check.
  • Do Loop: A loop that repeats a set of instructions for a specified number of times. Here, the loop goes through each variable in the array.
  • i: The loop counter, which keeps track of the current position in the array.
  • dim(): A function that returns the number of elements in the array.
  • Element: Each individual variable inside an array.
  • Incrementing the Counter: Adding 1 to a counter each time a condition is met.
  • Drop: A statement used to remove unnecessary variables (like the loop index i) from the final dataset.

Conclusion

This guide explains how to use arrays and loops in SAS to count variables that meet certain conditions. The array simplifies the process by allowing us to group variables and apply the same logic to all of them at once, while the loop checks each variable and updates the counter accordingly. This technique is particularly useful in data reporting and analysis where we need to quickly summarize or identify trends across multiple data points.