What is the Stata command to generate a variable that would take the initial value of the other variable?

[Faradj Koliev]

Dear all,

I have panel covering the period 1970-2010 with country-year being the unit of analysis. The data looks something like this:

country	year	X
A	1970	12
A	1971	9
B	1970	8
B	1971	11
B	1972	13
B	1973	4
C	1970	5
C	1971	3
C	1972	8

I would like to generate a variable X1 in Stata that would take the first value of X( that is in 1970!) for the whole period. So for example, the X1 for country B should be "8" for all years. To illustrate this:

country	year	X	X1
A	1970	12	12
A	1971	9	12
B	1970	8	8
B	1971	11	8
B	1972	13	8
B	1973	4	8
C	1970	5	5
C	1971	5	5
C	1972	5	5

I've tried different things with "generate X1= if" what I can't come up how to solve this. Anyone here who can help me with this?

[Justin Niakamal]

Try

bys country: gen x1 = x[1]

Alternativley,

sort country year
by country: gen x1 = x[1]

[Faradj Koliev]

Dear Justin: many thanks! It worked.

[Joro Kolev]

Try

bys country: gen x1 = x[1]

Alternativley,

sort country year
by country: gen x1 = x[1]

The second syntax delivers what Faradj Koliev wants to do. The first syntax is
1. not equivalent to the second syntax,
2. is very dangerous as it might, or might not deliver the intended outcome.
3. depends on whatever sort order you found your variables in (so whether it delivers or not, depends on the state in which you found your data).

Here is an example where the first syntax goes wrong:

. clear

. *(3 variables, 9 observations pasted into data editor)

. bys country: gen x1 = x[1]

. gen u = uniform()

. sort country u

. bys country: gen x11 = x[1]

. list, clean

       country   year    x   x1          u   x11  
  1.         A   1971    9   12   .1779098     9  
  2.         A   1970   12   12    .327647     9  
  3.         B   1970    8    8   .2569509     8  
  4.         B   1973    4    8   .6950182     8  
  5.         B   1972   13    8   .7894226     8  
  6.         B   1971   11    8   .7955964     8  
  7.         C   1971    3    5   .2781929     3  
  8.         C   1972    8    5    .461437     3  
  9.         C   1970    5    5   .9061013     3  

.

[Joro Kolev]

The one line short syntax equivalent to

 sort country year

by country: gen x1 = x[1]

[/CODE]

is

  
 bys country (year): gen x1 = x[1]

[Faradj Koliev]

Thanks, this turned out to be very useful in my case. I thought they all were sorted accordingly but I was wrong.

[Justin Niakamal]

Error on my part. Thanks for catching that Joro Kolev.