dropping observation for dates

[Qazi Qureshi]

Dear Statalist users

I am working on Pandemic Crisis. I need to drop all those firms/observations that have YEDate from 1 February 2020 to 31 May 2020 which belong to Data_Year 2019. I want to keep all those firms that have YEDate in these months for other periods, but not for Data_Year 2019.

I am using

drop if Data_Year==2019 & YEDate=="2/1/2020"

But it says

(0 observations deleted)

even though there are observations with this YEDate.

Can you please help me?

Thanks
Qazi

* Example generated by -dataex-. To install: ssc install dataex
clear
input str10 YEDate int Data_Year
"  1/1/2019" 2018
"  1/1/2021" 2020
"  1/1/2022" 2021
"  1/1/2022" 2021
"  1/1/2022" 2021
"  1/1/2022" 2021
"  1/1/2022" 2021
"  1/2/2020" 2019
"  1/2/2021" 2020
"  1/2/2021" 2020
"  1/2/2021" 2020
"  1/2/2022" 2021
"  1/2/2022" 2021
"  1/2/2022" 2021
"  1/2/2022" 2021
"  1/2/2022" 2021
"  1/2/2022" 2021
"  1/2/2022" 2021
"  1/2/2022" 2021
"  1/3/2019" 2018
"  1/3/2020" 2019
"  1/3/2021" 2020
"  1/3/2021" 2020
"  1/3/2021" 2020
"  1/3/2021" 2020
"  1/4/2019" 2018
"  1/4/2020" 2019
"  2/1/2020" 2019
"  2/2/2019" 2018
"  2/2/2020" 2019
"  2/3/2018" 2017
"  2/3/2019" 2018
"  2/4/2018" 2017
"  3/1/2018" 2017
"  3/1/2020" 2019
"  3/2/2019" 2018
"  3/3/2018" 2017
"  3/3/2021" 2020
"  3/3/2022" 2021
"  3/5/2022" 2021
"  3/6/2021" 2020
"  3/7/2020" 2019
"  3/9/2019" 2018
"  4/1/2018" 2017
"  4/1/2018" 2017
"  4/1/2019" 2018
"  4/1/2019" 2018
"  4/2/2018" 2017
"  4/2/2018" 2017
"  4/2/2021" 2020
"  4/2/2022" 2021
"  4/2/2022" 2021
"  4/2/2022" 2021
"  4/3/2020" 2019
"  4/3/2020" 2019
"  4/3/2021" 2020
"  4/3/2021" 2020
"  4/3/2021" 2020
"  4/4/2021" 2020
"  4/4/2021" 2020
"  4/4/2021" 2020
"  4/5/2020" 2019
"  5/1/2021" 2020
"  5/1/2021" 2020
"  5/2/2020" 2019
"  5/2/2020" 2019
"  5/2/2021" 2020
"  5/2/2021" 2020
"  6/2/2019" 2018
"  6/3/2018" 2017
"  7/1/2017" 2017
"  7/1/2017" 2017
"  7/1/2017" 2017
"  7/1/2017" 2017
"  7/1/2017" 2017
"  7/1/2018" 2018
"  7/1/2018" 2018
"  7/1/2018" 2018
"  7/1/2021" 2021
"  7/2/2017" 2017
"  7/2/2020" 2020
"  7/3/2021" 2021
"  7/3/2021" 2021
"  7/3/2021" 2021
"  8/1/2020" 2020
"  8/3/2018" 2018
"  9/1/2018" 2018
"  9/1/2018" 2018
"  9/2/2017" 2017
"  9/2/2017" 2017
" 1/24/2021" 2020
" 1/25/2020" 2019
" 1/25/2020" 2019
" 1/25/2020" 2019
" 1/26/2019" 2018
" 1/26/2019" 2018
" 1/26/2019" 2018
" 1/26/2019" 2018
" 1/26/2020" 2019
" 1/27/2018" 2017
end

[Rich Goldstein]

thank you for using -dataex- which allows one to see that your YEDate variable has leading spaces; so, if you use the following before your -drop- command you will find that there are observations that are dropped:

replace YEDate=strtrim(YEDate)

[Ken Chui]

It's because you have leading spaces, and those spaces count as a valid character. Try:

replace YEDate = trim(YEDate)
drop if Data_Year==2019 & YEDate=="2/1/2020"

However, more importantly, this is not an ideal way to code it because you will have to write one line for each date to be deleted. I'd suggest create a numerical date, and use logical condition to delete the cases:

* Alternative approach
gen new_date = date(YEDate, "MDY")
format new_date %td
drop if Data_Year == 2019 & new_date > date("2/1/2020", "MDY") & new_date < date("5/31/2020", "MDY")

[Qazi Qureshi]

Dear Rich and Ken

Thank you so much. It worked like a charm.
THANK YOU!

Warmest regards