topic Compare dates but only up to the same length in New SAS User

Compare dates but only up to the same length

gsk — Fri, 08 Nov 2019 21:19:18 GMT

Is there a quick way to compare two dates but only up to the same lengths, whichever the shorter length is between the two?

For example, if we compare date A and date B, and if date A is 2019-07-08 and date B is 2019-07-08T10:30, then SAS would say date B is bigger after comparing 2019-07-08 and 2019-07-08T10:30. Can we ask SAS to compare only up to length=10 (compare 2019-07-08 vs. 2019-07-08 instead of 2019-07-08 vs. 2019-07-08T10:30)?

This rule would apply to any lengths of the two dates in the same format: if we have two dates 2019-07-08T08:09:11 and 2019-07-08T08:08, then SAS would drop seconds for the first date and compare 2019-07-08T08:09 vs 2019-07-08T08:08.

Re: Compare dates but only up to the same length

novinosrin — Fri, 08 Nov 2019 21:22:51 GMT

HI @gsk Are your date and datetime variables numeric variables formatted in the way you have shown or those are character variables. Can you check using proc contents plz

Re: Compare dates but only up to the same length

Reeza — Fri, 08 Nov 2019 21:26:35 GMT

Use the colon modifier in your comparison, assuming you have character variables.

if date1 =: date2 then do;

.....


end;

You can compare only a specified prefix of a character expression by using a colon (:) after the comparison operator. SAS truncates the longer value to the length of the shorter value during the comparison. In the following example, the colon modifier after the equal sign tells SAS to look at only the first character of values of the variable LastName and to select the observations with names beginning with the letterS:

https://documentation.sas.com/?docsetId=lrcon&docsetTarget=p00iah2thp63bmn1lt20esag14lh.htm&docsetVersion=9.4&locale=en#p1vu0ts68u42xun141p7vt4ne29k

Re: Compare dates but only up to the same length

ballardw — Fri, 08 Nov 2019 23:22:35 GMT

Make sure that your dates, times and datetime variables are actual SAS date, time or datetime variables. These would show in proc contents or the data set description as 1) numeric values and 2) a format similar to Date9, MMDDYY10, YYMMDD10 for dates, TIME. for time values and DATETIME or E8601 and such.

Then when you need to compare "bits" of the values there are functions such as

If datevariable = datepart (datetimevariable)

if timevariable = timepart (datetimevariable)

or even use of the date functions:

If 12 = month(datepart(datetimevariable)); To get December records.

Re: Compare dates but only up to the same length

gsk — Fri, 08 Nov 2019 21:31:48 GMT

Thank you for the response! They are both character variables with length=20. Dates are in 2019-07-12 format, and hour, min, and sec come after T with colons (i.e. T14:29:30) if there is any. There doesn't need to be all components of year, month, date, hour, min or sec. A date could have only the year and month or can be missing.

Re: Compare dates but only up to the same length

novinosrin — Fri, 08 Nov 2019 21:34:38 GMT

Hi @gsk Why not doing it clean with a yymmdd10. informat?

data test;
date_A='2019-07-08';
date_B= '2019-07-08T10:30';
if input(date_A,yymmdd10.)=input(date_B,yymmdd10.) then output;
run;

Re: Compare dates but only up to the same length

gsk — Fri, 08 Nov 2019 21:46:27 GMT

But there could be cases like 2019-07-08T03 vs 2019-07-08T03:08 or 2017-03-14T21:33:20 vs 2017-03-14T21:33.

Re: Compare dates but only up to the same length

Reeza — Fri, 08 Nov 2019 21:48:03 GMT

Did you try my solution?

Re: Compare dates but only up to the same length

gsk — Fri, 08 Nov 2019 21:49:47 GMT

Sorry, not yet! I will in a bit!

Re: Compare dates but only up to the same length

novinosrin — Fri, 08 Nov 2019 22:07:25 GMT

Hi @gsk So what. You are only comparing the first 10 chars in your words length=10 and I would call them a width of 10 in a informat, Therefore what is after 10 chars in my opinion is garbage for SAS's informat yymmdd10.

And the date check becomes real and safe

data test;
date_A='2019-07-08T03 ';
date_B= '2019-07-08T03:08 ';
if input(date_A,yymmdd10.)=input(date_B,yymmdd10.) then output;
run;

Re: Compare dates but only up to the same length

art297 — Fri, 08 Nov 2019 22:23:26 GMT

I agree with @Reeza's suggestion but, to account for leading and trailing blanks, I think you will want to add the strip function to the variables you're comparing. E.g., try the following code:

data have;
  input (date1 date2) ($20.);
  if _n_ eq 3 then date1=' '||trim(date1);
  if date1 =: date2 then x=1;
  if trim(date1) =: trim(date2) then y=1;
  if strip(date1) =: strip(date2) then z=1;
  cards;
2019-07-08T08:08:11 2019-07-08T08:08
2019-07-08T08:08    2019-07-08T08:08:11
2019-07-08T08:08    2019-07-08T08:08:11
;
run;

Art, CEO, AnalystFinder.com

Re: Compare dates but only up to the same length

gsk — Sat, 09 Nov 2019 15:14:25 GMT

Thank you everyone!

Either input(dateA, yymmdd10.)=input(dateB,yymmdd10.) or dateA=:dateB works

In the end, I did strip(dateA)=:strip(dateB). Thanks a lot!