Drop duplicates depending on two variables

[Guest]

Hi,

I am totally new to Stata (Version 17.0). I´ve got a data set icluding the variables ticker (some kind of ID Code for each company, ZOTS and ZY in the extract below) and anndats (announcement dates) as well as multiple other variables.
Now I need to drop all observations, where ticker and anndats are the same.

Here is an extract from list ticker anndats:

ZOTS 03nov2015
ZOTS 16feb2016
ZOTS 16feb2016
ZOTS 04may2016
ZOTS 04may2016
---------------------------
ZY 15nov2016
ZY 22feb2017
ZY 22feb2017
ZY 16may2017


Like, for example, i want to drop the third, the fifth and the eigth row, but keep the rest. How do I do that?

[Bruce Weaver]

Hello Guest. Welcome to Statalist. This FAQ should help you with your problem:

• https://www.stata.com/support/faqs/d...-observations/

[Nick Cox]

Bruce Weaver That FAQ is flagged as for versions before 8. This is possible in 17.

 
* Example generated by -dataex-. For more info, type help dataex
clear
input str4 ticker float(anndats whatever)
"ZOTS" 20395 1
"ZOTS" 20500 2
"ZOTS" 20500 3
"ZOTS" 20578 4
"ZOTS" 20578 5
"ZY"   20773 6
"ZY"   20872 7
"ZY"   20872 8
"ZY"   20955 9
end
format %td anndats
[
. duplicates drop ticker anndats, force

Duplicates in terms of ticker anndats

(3 observations deleted)

. l

     +-------------------------------+
     | ticker     anndats   whatever |
     |-------------------------------|
  1. |   ZOTS   03nov2015          1 |
  2. |   ZOTS   16feb2016          2 |
  3. |   ZOTS   04may2016          4 |
  4. |     ZY   15nov2016          6 |
  5. |     ZY   22feb2017          7 |
     |-------------------------------|
  6. |     ZY   16may2017          9 |
     +-------------------------------+

.

[Bruce Weaver]

Bruce Weaver That FAQ is flagged as for versions before 8. This is possible in 17.

Ah yes, of course. I should have spotted that.

This UCLA page has more up-to-date examples.