Dates Saad Rais

Ministry of Health and Long-Term Care

Nov 20, 2015

SAS Dates are like sour grapes…

What do we use dates for?

Data query by period Measure duration

Time indicators Forecasting Modelling

Rates Time-trend

Merge by date Frequency tables

Before-after analysis Longitudinal data analysis

You will learn how to:

• Create a date variable

• Display a date in a certain way (formats)

• Read in a date from a text file

• Convert a string variable into a date variable

• Calculate duration between dates

• Parse dates into its components

Creating a date variable

• Date variables are numeric variables 0 = Jan 1 1960 1 = Jan 2 1960 -1 = Dec 31 1959

• What is the number for today’s date? – Use today () function %put %sysfunc(today ());

20411

• What is the number for my birthday (or any day)? – use MDY (month, day, year) function %put %sysfunc(mdy(2,28,1970));

3711

– use date in quotes and a ‘d’ %let sas_day = “19NOV2015"d;

%put %sysfunc(putn(&sas_day, 8.0));

20411

Displaying dates a certain way: formats

• Dates are stored as numeric values

0 = January 1, 1960

• Numeric values may be ‘externally’ represented by a format

• List of date formats can be found here: https://support.sas.com/documentation/cdl/en/etsug/60372/HTML/default/viewer.htm#etsug_intervals_sect010.htm

Some date formats

ID values Periodicity FORMAT Example

SAS date annual YEAR4. 1991

quarterly YYQC6. 1991:4

monthly MONYY7. OCT1991

weekly WEEKDATX23. Thursday, 17 Oct 1991

daily DATE9. 17OCT1991

SAS datetime hourly DATETIME10. 17OCT91:14

minutes DATETIME13. 17OCT91:14:45

seconds DATETIME16. 17OCT91:14:45:32

What SAS dates can look like

Sample anatomy of a date format

• DDMMYY = order of day month, year – Could be YYMMDD or something else

• x = separator (default = dash) – B = blank C = colon D = dash N = none P= period

S = slash

• w = character width including separator (default = 8)

DDMMYYxw.

Sample output of date formats

• Examples: %let d = 18788 /* = “10JUN2011"d*/;

%put %sysfunc(putn(&d,yymmdd.));

11-06-10

%put %sysfunc(putn(&d,yymmdds.));

11/06/10

%put %sysfunc(putn(&d,yymmdds10.));

2011/06/10

%put %sysfunc(putn(&d,ddmmyys10.));

10/06/2011

%put %sysfunc(putn(&d,yymmdd7.));

110610

Reading in dates from a flat file

• Step 1: Identify the date informat

Reading in dates from a flat file

• Step 2a: Decide on the format (point & click)

Reading in dates from a flat file

• Step 2b: Decide on the format (code)

Reading in dates from a flat file

• Step 3: Check that data was imported correctly

Converting string variable to date variable

Converting string variable to date variable

• Step 1: Know the string variable informat

• Step 2: Create a numeric variable out of the string variable using ‘input’ function and informat

• Step 3: Specify the date format for the numeric date variable

Converting string variable to date variable

data rpdb;

set rpdb.rpdb_personal_charcs

(obs = 10 keep = create_tmestmp);

create_tmestmp_new =

input(create_tmestmp, ymddttm20.);

create_tmestmp_new_formatted =

create_tmestmp_new;

format create_tmestmp_new_formatted

datetime19.;

run;

Converting string variable to date variable

Performing calculations with dates

• E.g., Age (integer or continuous)

• Methods:

– (Ref_date – DOB + 1) / 365.25

– YRDIF Function, using ‘AGE’ parameter value

– Formula that uses INTCK function (counting the number of completed months)

• For continuous age, add the proportion of the year completed (macro provided in appendix A)

Performing calculations with dates

%let start_dt = "29feb2000"d; /*DOB*/

%let end_dt = "28feb2050"d; /*50TH BDAY?*/

data age;

age1 = (&end_dt - &start_dt + 1)/365.25;

age2 = yrdif(&start_dt, &end_dt, 'AGE');

%age_continuous (agevar=age3, dob=&start_dt, eventdate=&end_dt);

age1_int = int(age1);

age2_int = int(age2);

age3_int = int(age3);

age4_int = int((intck('month',&start_dt,&end_dt)- (day(&end_dt)<day(&start_dt)))/12);

run;

Parsing dates into its components

• Datepart(datetime_var)

• Year(date_var)

• Qtr(date_var)

• Month(date_var)

• Day(date_var)

Parsing dates into its components

The End

For more information, contact:

Saad Rais Saad.rais@ontario.ca

Appendix A: Macro to calculate continuous age

%macro age_continuous (agevar=,dob=,eventdate=);

m_age_int = floor((intck('month',&dob.,&eventdate.)-

(day(&eventdate.)<day(&dob.)))/12);

m_prior_bday_correction = (month(&dob.)eq 2)*(day(&dob.)eq 29)*

(put(MDY(12,31,(year(&dob.)+m_age_int)),JULDAY.)eq "365");

m_prior_bday = MDY(month(&dob.+m_prior_bday_correction),

day (&dob.+m_prior_bday_correction),

year (&dob.)+m_age_int);

m_next_bday_correction = (month(&dob.)eq 2)*(day(&dob.)eq 29)*

(put(MDY(12,31,(year(&dob.)+m_age_int+1)),JULDAY.)eq "365");

m_next_bday = MDY(month(&dob.+m_next_bday_correction),

day (&dob.+m_next_bday_correction),

year (&dob.)+m_age_int+1);

&agevar. = m_age_int+((&eventdate.-m_prior_bday)/(m_next_bday-m_prior_bday));

drop m_age_int m_prior_bday_correction m_prior_bday m_next_bday_correction

m_next_bday;

%mend age_continuous;

Courtesy: http://www.wuss.org/proceedings09/09WUSSProceedings/papers/cod/COD-Adams.pdf