combine Several observations to one observation in a given year

[Mohamed Mahmoud]

Dear all,

I need to get the SUM of Var 1. for each ID observation in 2016,

for example, A person who has ID 1 has a total of $100 for Var.1 and $500 for Var. 2 in 2016, and so on

I need to have one observation for each ID , by summing up the observations for this ID in this year

What is the command should I use ?

	ID	Year	Var. 1	Var. 2
	1	2016	50	100
	1	2016	30	200
	1	2016	20	300
	2	2016	60
	2	2016
	2	2016
	1	2017
	1	2017
	1	2017

[Nick Cox]

* Example generated by -dataex-. For more info, type help dataex
clear
input byte id int year byte var1 int var2
1 2016 50 100
1 2016 30 200
1 2016 20 300
2 2016 60  42
2 2016 40  58
end

collapse (sum) var1 var2, by(id year)

list

     +-------------------------+
     | id   year   var1   var2 |
     |-------------------------|
  1. |  1   2016    100    600 |
  2. |  2   2016    100    100 |
     +-------------------------+

[Mohamed Mahmoud]

Thanks Nick Cox,

one more question please

What is the code that used to generate variable called " average assets" ffirm-yearirm year observation

Note: Average assets = (assets current year + assets previous year) / 2


the data format is

firm ID	year	total assets	average assets
1	2010	10	.
1	2011	20	= 15
1	2012	25	=22.5
2	2010	30	=.
2	2011	50	=40
2	2012	80	= 65

Many thanks