How to Find the First and Last Missing Value in a Specific Row in SAS

Finding the first and last missing value in a specific row in SAS can be a complex task, but with the right approach, it can be accomplished efficiently. This article provides a detailed step-by-step guide on how to achieve this using a combination of the IFN function and array processing. By the end of this article, you will understand the process and be able to apply it to your own data.

Step 1: Create a Sample Dataset

First, let's create a sample dataset with some missing values.

data mydata; input id value1 value2 value3 value4; datalines; 1 10 . 20 . 2 . 30 . 40 3 50 60 . . 4 . . . 80 ; runtime mydata;

Step 2: Use Arrays to Identify Missing Values

To find the first and last missing values in a specific row, you can use an array to loop through the values in a specific row and find the first and last missing values. The following code demonstrates this approach.

data missing_values; set mydata; array values {} value1-value4; / /* Adjust the range based on your dataset */ / first_missing .; last_missing .; / /* Loop through the array to find first and last missing values */ / do i 1 to dim(values); if values[i] . then do; if first_missing . then first_missing i; /
/* Store the index of the first missing */ /
last_missing i; /
/* Update the index of the last missing */ /
end; end; / /* Output the result */ / if first_missing ne . then
first_missing_value values[first_missing];
else
first_missing_value .;
if last_missing ne . then
last_missing_value values[last_missing];
else
last_missing_value .;
drop i first_missing last_missing;
run;

Explanation

Array Declaration: array values {} value1-value4 creates an array of the specified variables.Loop: do i 1 to dim(values) loop iterates through each element of the array.First and Last Missing Logic: first_missing captures the index of the first missing value, while last_missing updates with the index of each missing value found, ensuring it holds the last one encountered.Result Assignment: After the loop, you can assign the actual missing values to first_missing_value and last_missing_value based on their indices.Final Output: You can then view the results by running:

proc print datamissing_values;
runtime proc print;

Conclusion

By following these steps, you can effectively find the first and last missing values in a specific row in SAS. This method is particularly useful in data analysis and preprocessing tasks where understanding the distribution of missing values is crucial. Adjust the variable names and the number of array elements according to your dataset structure for best results.