Dates. Saad Rais. Ministry of Health and Long-Term Care Nov 20, 2015

Transcription

1 Dates Saad Rais Ministry of Health and Long-Term Care Nov 20, 2015

2 SAS Dates are like sour grapes

3 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

4 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

5 Creating a date variable Date variables are numeric variables 0 = Jan = Jan = Dec What is the number for today s date? Use today () function %put %sysfunc(today ()); 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

6 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:

7 Some date formats ID values Periodicity FORMAT Example SAS date annual YEAR quarterly YYQC :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

8 What SAS dates can look like

9 Sample anatomy of a date format DDMMYYxw. 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)

10 Sample output of date formats Examples: %let d = /* = 10JUN2011"d*/; %put %sysfunc(putn(&d,yymmdd.)); %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.));

11 Reading in dates from a flat file Step 1: Identify the date informat

12 Reading in dates from a flat file Step 2a: Decide on the format (point & click)

13 Reading in dates from a flat file Step 2b: Decide on the format (code)

14 Reading in dates from a flat file Step 3: Check that data was imported correctly

15 Converting string variable to date variable

16 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

17 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;

18 Converting string variable to date variable

19 Performing calculations with dates E.g., Age (integer or continuous) Methods: (Ref_date DOB + 1) / 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)

20 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); run; 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);

21 Parsing dates into its components Datepart(datetime_var) Year(date_var) Qtr(date_var) Month(date_var) Day(date_var)

22 Parsing dates into its components

23 The End For more information, contact: Saad Rais

24 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: