The use of Output and Retain here?

[Lulus]

https://communities.sas.com/t5/Base-SAS-Programming/delete-observation-based-on-previous-value/m-p/2...

Please help with the following unanswered quesiton.  this is more programming quesiton.  thank you in advance your help!

follwing the quesiton from the URL, 

however I have another silly question.

if delflag=0 then output;
if happen=1 then delflag=1;

in the above two statement,

the lines with delflag=0 have been written to the want dataset and

how does the next if clause still truncate the rest of observations against the same id?

and even leave the first "happen=1" in the dataset?

I am trying to learn this logic.  your response is very appreicated.

[FreelanceReinh · Accepted solution]

Hello @Lulus,

Here is what happens with each observation of your example dataset when mohamed_zaki's data step is executed (focusing on the three lines of code starting with "if"):

ID seq happen   comment
1   1    0      delflag is set to 0, obs. (incl. delflag) is written to WANT due to OUTPUT statement
1   2    0      delflag is still 0 due to RETAIN, obs. is written to WANT
1   3    1      delflag is still 0, obs. is written to WANT, delflag is set to 1
2   1    0      delflag is set to 0, obs. is written to WANT
2   2    1      delflag is still 0, obs. is written to WANT, delflag is set to 1
2   3    0      delflag is still 1, hence obs. is not written to WANT
2   4    1      delflag is still 1, hence obs. is not written to WANT, delflag is set to 1