How to Convert a Datetime to a SAS Date Format

You have probably already noticed that SAS provides two formats to store information about dates, namely as a Datetime variable or as a Date variable. So, to compare them, you need to convert a Datetime variable into a Date variable first. In this article, we explain how to do extract only the Date from a Datetime variable.

The DATEPART function in SAS converts a Datetime variable into a Date variable. This function takes as an argument a Datetime variable and returns only the Date part.

In this article, we look into more detail how to use the DATEPART function.

How to Convert a Datetime into a Date with the SAS DATEPART Function

The DATEPART function converts your Datetime variable into a Date variable and requires one argument. The argument is, obviously, a Datetime variable.

DATEPART(DateTime Variable)

Why Does the DATEPART Function Convert a Datetime into a Number

As you might know, SAS Datetime variables and Date variables are stored as the number of seconds (for Datetime) or days (for Dates) from the 1^st of January, 1960. So, if you use the DATEPART function, it returns the number of days between your date and the 1^st of January, 1960. For example:

DATEPART("31AUG2020:0:0:0"dt) --> 22.158

However, to make the results of the DATEPART function interpretable, we need to apply a Date format. In the example below, we extract the datepart of a Datetime variable and present the result in 4 ways:

• Without a format, i.e., the number of days from the 1^st of January, 1960.
• With the MM/DD/YYYY format, e.g., 08/31/2020
• With the YYYY/MM/DD format, e.g., 2020-08-31
• With the DATE9. format, e.g., 31AUG2020

For a complete list of Date formats, check out this page.

data work.my_ds;
	format my_datetime datetime23.;
	input my_datetime :datetime23.;
	datalines;
31AUG2020:0:0:0
01SEP2020:0:0:0
30SEP2020:0:0:0
15OCT2020:0:0:0
;
run;
 
data work.my_ds_format;
	set work.my_ds;
 
	my_date_no_format = datepart(my_datetime);
	my_date_mmddyyyy = datepart(my_datetime);
	my_date_yyyymmdd = datepart(my_datetime);
	my_date_date9 = datepart(my_datetime);
 
	format my_date_mmddyyyy mmddyy10.;
	format my_date_yyyymmdd yymmdd10.;
	format my_date_date9 date9.;
run;

Use the DATEPART Function to Filter Data

In the example above, we showed how to create a new Date variable extracting the datepart of a Datetime variable, and applying a format. You can also use the DATEPART function to filter your data. For example, we filter all observations until the 1^st of September, 2020.

data work.my_ds_filter;
	set work.my_ds;
 
	if datepart(my_datetime) le "01SEP2020"D 
	then output;
run;

As you can see we used a Date format to filter the data (“01SEP2020″D). However, in the output dataset work.my_ds_filter, then column my_datetime has still the Datetime format.

Use the DATEPART Function in Another Function

As mentioned before, you can’t compare a Datetime variable with a Date variable. However, some functions that use Date(time) variables as arguments require that all arguments are of the same type. So, how do you convert a Datetime into a Date variable in a function?

You can easily convert your Datetime variable into a Date variable within a SAS function. For example, below we use the DATEPART function within the INTCK function to calculate the number of days between two dates.

data work.my_ds;
	format my_datetime datetime23. my_date date9.;
	input my_datetime :datetime23. my_date :date9.;
	datalines;
31AUG2020:0:0:0 04SEP2020
01SEP2020:0:0:0 12OCT2020
30SEP2020:0:0:0 17NOV2020
15OCT2020:0:0:0 2JAN2021
;
run;
 
data work.diff_in_days;
	set work.my_ds;
 
	diff_in_days = intck("day", datepart(my_datetime), my_date);
run;

Do you know? How to Convert a Number into a SAS Date