Generate a week from a data and "xtset" the data

[Alberto Alvarez]

Dear Stata Users,
I have the sample of data attached below. I need to create a “week” date that goes from Wednesday till Wednesday. For this, I used the following code:

gen week_start = cond(dow(date) >= 3, date - dow(date) + 3, date - dow(date) - 4)

The problem is that it generates a date variable (with a difference of 7 between two dates) that I cant format into %tw, so that stata understands the id and time variable:

xtset permno week_start

Can you, please help me to resolve this issue.

* Example generated by -dataex-. To install: ssc install dataex
clear
input double permno long date
10000 9502
10000 9503
10000 9504
10000 9505
10000 9506
10000 9509
10000 9510
10000 9511
10000 9512
10000 9513
10000 9516
10000 9517
10000 9518
10000 9519
10000 9520
10000 9523
10000 9524
10000 9525
10000 9526
10000 9527
10000 9530
10000 9531
10000 9532
10000 9533
10000 9534
10000 9537
10000 9538
10000 9539
10000 9540
10000 9541
10000 9545
10000 9546
10000 9547
10000 9548
10000 9551
10001 9510
10001 9511
10001 9512
10001 9513
10001 9516
10001 9517
10001 9518
10001 9519
10001 9520
10001 9523
10001 9524
10001 9525
10001 9526
10001 9527
10001 9530
10001 9531
10001 9532
10001 9533
10001 9534
10001 9537
10001 9538
10001 9539
10001 9540
10001 9541
10001 9545
10001 9546
10001 9547
10001 9548
10001 9551
10001 9552
10001 9553
10001 9554
10001 9555
10001 9558
10001 9559
10001 9560
10001 9561
10001 9562
10001 9565
10001 9566
10001 9567
10001 9568
10001 9569
10001 9572
10001 9573
10001 9574
10001 9575
10001 9576
10001 9579
10001 9580
10001 9581
10001 9582
10001 9586
10001 9587
10001 9588
10001 9589
10001 9590
10001 9593
10001 9594
10001 9595
10001 9596
10001 9597
10001 9600
10001 9601
10001 9602
end
format %d date

[Clyde Schechter]

Stata has week variables, but I don't think they will be useful to you. They cannot be forced to begin on Wednesday, and in fact a new week always starts on January 1.

So I think you will have to just settle for week_start the way you have defined it.

That said, you will not be able to -xtset permno week_start- no matter what you do, because you will encounter the "repeated time values within panel" error: you have up to 7 observations per form for any week, because you have daily data.

[Nick Cox]

Clyde Schechter pointed out a key problem. Here are some more.

You shouldn't even try to format this new date as weekly. It's still a daily date. In particular,

1. Today is a Wednesday and 21642 days after 1 January 1960. If you tell Stata that's a weekly date, then you're referring to the 21642nd week since 1 January 1960. That's a long way into the future.

2. Stata's weekly formats have no idea that weeks can span years and that there can be 53 weeks starting in a year, which is what your definition implies.

Weeks running from Wednesday to Wednesday are 8 days long and overlap. I guess you don't mean that.

Stata understands fine that daily dates can be 7 days apart. Just use the delta() option of tsset and xtset. That solves all your problems -- except the one Clyde pointed out.

---------------------------

PS You are not good at closing threads. Closing means reporting on the outcome, even if the report is that the code didn't work or you're still puzzled.

I looked at your recent posts and found that you closed none of the last four threads you started

https://www.statalist.org/forums/for...able-with-zero

https://www.statalist.org/forums/for...an-correlation

https://www.statalist.org/forums/for...erval-of-dates

https://www.statalist.org/forums/for...-certain-dates

I stopped there. That's a pattern. That is disappointing -- both to the people who answered you; why we should we bother in future with your questions?-- and to people who might read your posts and wonder what the outcome was.

[Alberto Alvarez]

Thank you for the response. I foget to mention that I will than drop duplicates by "permno week_start" (was my fault). I used your suggesting to use "delta" with xtset. My final code looks like:

xtset permno week_start, delta(7 )