Counting the number of days between two dates, excluding specific days of the week

[laura packel]

Hi,
I need to calculate the number of elapsed days between two dates (visitdate and new_apptdate) for each observation excluding certain days of the week. Here is what the data look like:
+-----------------------------------------------+
| id visitdate new_app~e daysa~pt |
|-----------------------------------------------|
40. | 00542KPP-4 25nov2016 25nov2016 0 |
41. | 00542KPP-4 17feb2017 17feb2017 0 |
42. | 00542KPP-4 12may2017 12may2017 0 |
43. | 00542KPP-4 10jul2017 07jul2017 3 |
44. | 00542KPP-4 10oct2017 02oct2017 8 |
|-----------------------------------------------|
45. | 00542KPP-4 17jan2018 21nov2017 57 |
46. | 00542KPP-4 13feb2018 14feb2018 -1 |
47. | 00751KLM-1 25may2016 . . |
48. | 00751KLM-1 31may2016 31may2016 0 |
49. | 00751KLM-1 28jun2016 28jun2016 0 |
|-----------------------------------------------|
50. | 00751KLM-1 26jul2016 26jul2016 0 |
+-----------------------------------------------+

The workdays package only excludes weekends and holidays - I need to also exclude Fridays, and for a subset of observations, Thursdays as well.
Thanks for any help you can provide.

[Leonardo Guizzetti]

No specific solution, but it sounds like you may want to investigate the use of business calendars, which were made for this purpose.

See:
1) the output of -help datetime_business_calendars-
2) https://blog.stata.com/2016/02/04/ha...ess-calendars/

[Scott Merryman]

Perhaps something like this:

clear
input str10 date1 str10 date2
3apr2020 16apr2021
3apr2020 15apr2021
4apr2020 16apr2021
1apr2020 15apr2021
end

gen mydate1=date(date1, "DMY")
gen mydate2=date(date2, "DMY")
format mydate* %td
drop date*
gen length = mydate2 - mydate1+1
gen number_of_weeks =floor(length/7)
gen remainder = mod(length, 7) 
//DOW starts at 0 = Sunday
gen dow_start= word(c(Weekdays), dow(mydate1)+1)
gen dow_end= word(c(Weekdays), dow(mydate2)+1)
gen last_dow = word(c(Weekdays), dow(mydate1+7))

gen number_of_fridays = number_of_weeks /// 
    +  cond(dow(mydate2)+1 -dow(mydate1+7)>0 /// 
    & dow(mydate2)>4 , 1,0)
list, ab(15)