st: calculating differences in variables in Longitudinal Data

[Alexander Zoran Dozet <zod_63@yahoo.se>]

Dear Statausers,

I have a small problem 
that I suppose is easy to resolve if one knows the ansewer. Although it 
probably is basic, I have tried to solve it by searching the internet 
and hitting the books, I have not succeded in finding an answer.

I have a dataset that looks like this:


Company                Year                    Variable1                Variable2                Variable3.........Variable54

Company1              2009                    60                            70                           80  
Company1              2010                    65                            72                           81

Company1              2011                    67                            71                           85

Company2              2009                    85                            80                           70

Company2              2010                    75                            85                           78

Company2              2011                    77                            88                           76

.
.
.
Company154


I hope the displayed data structure is kept in this e-mail.
Each company is occuring one time each year for each variable in the data 
set (panel data). My variable Company is in string form. I have not 
declared my dataset to be panel data. String is not allowed as an 
identifier.

I want to examine the difference between the 
year 2010 and 2011 for each company and for each variable and to create a new variable for each of the differences for 
example diffVar1, diffVar2,....

I would be much grateful for any help!

Best regards and cheers
Alexander Dozet

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