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st: Constructe a string variable

From   [email protected]
To   [email protected]
Subject   st: Constructe a string variable
Date   Wed, 16 Apr 2003 22:52:37 -0400

Dear Listers:

Suppose I have a string variable with 3 position on each observations.
Each of these observations contains some values range from 1-999.
obs1   1
obs2   12
obs3   123
(though all entries are numerical, but variable X is of string format)

My purpose is to reconstruct this variable to be the following formate:
obs1   001
obs2   023
obs3   345

i.e. I want to replace the left postition for each observation with "0" if 
nothing here.

I have tried the following method:

gen str1 X1=substr(X, 1, 1)
gen str2 X2=substr(X, 2, 1)
gen str3 X3=substr(X, 3, 1)

my idea is that if I can divide original variable(X) into 3 pieces, and then I 
can replace the missing( or " ") into 0, and then re-combine the variable.

However, in the above data example.
the X1 (=substr(X,1,1) is always equal to: 

obs1 1
obs2 2
obs2 3

(the corerct one should be:
obs2 3

That means, the function of -string- or -substr- in Stata will always return 
the first values of that observations no matter its' real position.
I am just wondering whether anyone knows an easier function or command to deal 
with that?

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