Working with Dates and Times in SAS: Cleaning and Transformation

Introduction

Working with dates and times in SAS can often be challenging due to various formats, discrepancies, and the need for precise cleaning and transformation. Whether you’re managing timestamps, performing date arithmetic, or converting date formats, SAS provides a powerful toolkit for transforming and cleaning time-related data.

In this article, we will explore techniques to handle dates and times effectively in SAS, focusing on cleaning and transforming your data to ensure it’s ready for analysis. We’ll dive into the use of SAS date and time functions, address common pitfalls, and provide practical examples that can help you streamline your data wrangling process.

Understanding SAS Date and Time Variables

In SAS, date and time variables are represented as numerical values. However, there are distinct differences between SAS date values (which count the number of days since January 1, 1960) and SAS time values (which count the number of seconds since midnight).

• SAS Date: Represents dates, with values measured in days.
• SAS Time: Represents times, with values measured in seconds.
• SAS Datetime: Combines both date and time into one value, measured in seconds.

Working with dates and times in SAS requires understanding how these values are stored and how they can be manipulated using different functions. In this section, we will show you how to clean and transform date and time data for better usability.

Step 1: Converting String Dates into SAS Date Format

One of the most common tasks when working with dates in SAS is converting string representations of dates into SAS date values. SAS provides multiple ways to do this using INPUT(), DATE9., and other date formats.

Example: Converting String Date to SAS Date Format

data example;
    input string_date $10.;
    date_value = input(string_date, date9.);
    format date_value date9.;
datalines;
01JAN2020
15MAR2021
28JUL2019
;
run;

In the example above:

• INPUT() converts the string date (string_date) into a SAS date value.
• The DATE9. format is used to interpret the string date in the format DDMMMYYYY.

This conversion is essential when your raw data consists of dates stored as strings, which need to be transformed into a date format for analysis.

Step 2: Extracting Date and Time Components

Often, your data may require you to extract individual components, such as the day, month, year, or even the hour and minute from a datetime value. This can be done using SAS date and time functions.

Example: Extracting Date Components

data example;
    input datetime_value datetime.;
    day = day(datetime_value);
    month = month(datetime_value);
    year = year(datetime_value);
    format datetime_value datetime20.;
datalines;
01JAN2020:12:00:00
15MAR2021:08:30:00
28JUL2019:14:45:00
;
run;

In this example:

• DAY(), MONTH(), and YEAR() functions are used to extract the respective date components from a datetime_value.

Similarly, you can use functions like HOUR(), MINUTE(), and SECOND() to extract time components from a SAS time or datetime value.

Step 3: Handling Missing Date and Time Values

Missing date and time values are common in datasets, and it is important to handle them properly. SAS uses a specific value (., for dates and times) to represent missing data. If you have missing date or time values in your dataset, there are several ways to manage them.

Example: Checking and Replacing Missing Date Values

data example;
    input date_value : date9.;
    if date_value = . then date_value = '01JAN1900'd;
    format date_value date9.;
datalines;
15MAR2021
.
28JUL2019
;
run;

In this example:

• We check if the date_value is missing and replace it with a default date (01JAN1900).

This strategy ensures that your analysis does not fail due to missing date values, and provides a fallback date if necessary.

Step 4: Date Arithmetic

Once your dates are properly formatted, you can perform various arithmetic operations on them, such as calculating the difference between two dates or adding a specific number of days to a date.

Example: Calculating Date Differences

data example;
    input start_date : date9. end_date : date9.;
    days_diff = end_date - start_date;
    format start_date end_date date9.;
datalines;
01JAN2020 15JAN2020
01MAR2021 15MAR2021
28JUL2019 05AUG2019
;
run;

In this example:

• end_date - start_date computes the difference between two dates in days. The result is stored in days_diff.

You can also add or subtract days to/from a date using simple arithmetic:

data example;
    input start_date : date9.;
    future_date = start_date + 30;  /* Adds 30 days */
    format start_date future_date date9.;
datalines;
01JAN2020
15MAR2021
28JUL2019
;
run;

Here, 30 days are added to each start_date to create a future_date.

Step 5: Converting Between Date and Time Formats

In some scenarios, you may need to convert between date and time formats. SAS provides functions to convert datetime values into date-only values and vice versa.

Example: Converting Datetime to Date

data example;
    input datetime_value : datetime20.;
    date_value = datepart(datetime_value);
    format datetime_value date9. date_value date9.;
datalines;
01JAN2020:12:00:00
15MAR2021:08:30:00
28JUL2019:14:45:00
;
run;

In this example:

• DATEPART() extracts the date portion from a datetime_value (i.e., removing the time part).

Similarly, you can convert a date into a datetime value by using the DHMS() function, which combines date and time components into a datetime value.

Step 6: Time Zones and Date/Time Formats

When working with data from different time zones or regions, SAS allows you to handle time zone conversions using specific formats and functions. The TZD and TZD9. formats can help you work with time zone data effectively.

For instance, if you need to adjust a datetime value from one time zone to another, you can use the timezone() function to perform the conversion.

Best Practices for Working with Dates and Times in SAS

1. Use the Correct Formats: Always ensure you’re using the right formats (e.g., DATE9., DATETIME20.) for your data types to avoid misinterpretation of date and time values.
2. Handle Missing Data Early: Missing date or time values should be handled right at the beginning to avoid errors during analysis.
3. Convert String Dates Before Use: If your data has string representations of dates, convert them into SAS date formats as soon as possible.
4. Use Date Arithmetic Wisely: For tasks like calculating age or duration, SAS date functions allow for efficient arithmetic operations.

External Resources

For more details on date and time functions in SAS, you can refer to the following resources:

• SAS Date Functions Documentation
• SAS Time Functions Documentation
• SAS Guide to Dates and Times

FAQs

1. What are the common formats for SAS dates?
   Common formats for SAS dates include DATE9., MMDDYY10., and DDMMYY10.. These formats represent the date in various styles.
2. How do I handle time zones in SAS?
   You can use the TZD or TZD9. formats to handle time zone information and adjust datetime values accordingly.
3. How do I calculate the difference between two dates in SAS?
   You can subtract one date from another using simple arithmetic, and SAS will return the difference in days.
4. How do I convert a string to a date in SAS?
   Use the INPUT() function to convert a string into a SAS date value, along with the appropriate date format (e.g., DATE9.).
5. Can I add months or years to a date in SAS?
   Yes, you can use INTNX() to add months or years to a date, like so: future_date = intnx('month', start_date, 2).
6. What is the difference between a date and datetime in SAS?
   A SAS date represents the number of days since January 1, 1960, while a SAS datetime includes both date and time information in seconds.
7. How do I extract the year from a datetime value?
   You can use the YEAR() function on a datetime value to extract the year component.
8. What happens if my dataset has missing date values?
   Missing date values are represented as . in SAS. You can handle them using conditional statements to replace or flag missing values.
9. How can I convert a datetime to just a date?
   Use the DATEPART() function to extract the date from a datetime value.
10. What function can I use to calculate the current date and time?
    Use TODAY() for the current date and DATETIME() for the current date and time.

By following these best practices and leveraging SAS’s powerful date and time functions, you can efficiently clean and transform your time-related data, ensuring accuracy and consistency throughout your analysis.