Conditional Variable Update in Stata

Stata Function to Update Variable Based on Condition

Introduction

This Stata script defines a function to conditionally calculate a new variable UEXPVIS based on the value of another variable GAGEBC. If GAGEBC is greater than or equal to 35, UEXPVIS will be computed as (GAGEBC - 35) + 9.

Code Snippet

* Stata code snippet to conditionally update the variable UEXPVIS based on the value of GAGEBC

** Ensure necessary variable(s) exist **
cap assert inlist("GAGEBC", `: varlist') & inlist("UEXPVIS", `: varlist')  // Check if variables exist
if _rc == 198 {  // 198 is the return code for 'no variables defined'
    display "Required variables (GAGEBC, UEXPVIS) do not exist in the dataset. Please check."
    exit 1
}

** Validate input data **
foreach var in GAGEBC UEXPVIS {
    assert missing(`var') | `var' >= 0  // Ensure variables are non-missing and non-negative
    if _rc {
        display "`var' contains invalid data. Please correct and re-run."
        exit 1
    }
} 

** Conditionally compute UEXPVIS **
gen UEXPVIS = .  // Initialize UEXPVIS to missing values
replace UEXPVIS = (GAGEBC - 35) + 9 if GAGEBC >= 35

** Provide feedback to the user **
di "Variable UEXPVIS has been updated based on the condition GAGEBC >= 35."

Explanation

1. Variable Existence Check:

   • Ensure that the GAGEBC and UEXPVIS variables exist in the dataset. If not, an error message is displayed, and the script exits.

2. Input Validation:

   • Check that the GAGEBC and UEXPVIS variables contain non-missing and non-negative values. If any invalid data is detected, an error message is displayed, and the script exits.

3. Conditional Calculation of UEXPVIS:

   • Initialize UEXPVIS to missing values.
   • Update UEXPVIS based on the condition (GAGEBC - 35) + 9 if GAGEBC is greater than or equal to 35.

4. User Feedback:

   • Print a message indicating that the UEXPVIS variable has been successfully updated.

Usage Example

* Example usage of the conditional computation script 

* Load sample data
sysuse auto, clear

* Let's assume 'GAGEBC' exists and needs conditional computation
gen GAGEBC = 40  // Example value; in practice, this would be part of dataset

* Run the above script to compute UEXPVIS
* The user would copy and paste the above script into the Stata command window or run from a .do file

Conclusion

This script ensures robust handling of input data and conditionally updates the variable UEXPVIS based on the specified condition, with comprehensive checks and validations in place to guide users through any potential issues with input data. For more insights and courses on data analysis and best practices, consider exploring resources on the Enterprise DNA Platform.