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AW: st: on data transformation


From   rado645-bg@yahoo.de
To   statalist@hsphsun2.harvard.edu
Subject   AW: st: on data transformation
Date   Mon, 25 Jul 2011 14:25:11 +0100 (BST)

Hi Nick,

I have just had a look at your code. Thanks a lot for your feedback. I am trying 
to run the command but I am stuck with the loop: Could you please help me with 
that:


I have the following code:

//here I create the "occurred" variable

bysort id year (failed) : gen occurred = failed[_N]
*keep if occurred

//leave observations in the year of failure and the previous one (I follow the 
code from your last message

replace tag = occurred
levelsof x, local(X)

foreach x of local X {
      levelsof year if x == `x' & occurred, local(Y)
      foreach y of local Y {
            replace tag = 1 if year == `y' - 1 & x == `x'
        }
}

keep if tag


I wonder if I shall replace x and y with other variables here.Or shall I run the 
loop part as an ado file? In such case, what shall x and y be? 


Many thanks in advance.

Best,
Rado




----- Ursprüngliche Mail ----
Von: Nick Cox <njcoxstata@gmail.com>
An: statalist@hsphsun2.harvard.edu
Gesendet: Mittwoch, den 20. Juli 2011, 22:44:36 Uhr
Betreff: Re: st: on data transformation

Much depends on whether years with the event can only occur once for
each object.

Let's assume not to make the problem more challenging. Here is one way
to do it:

gen tag = occurred
levelsof x, local(X)

foreach x of local X {
       levelsof year if x == `x' & occurred, local(Y)
       foreach y of local Y {
            replace tag = 1 if year == `y' - 1 & x == `x'
        }
}

keep if tag

On Wed, Jul 20, 2011 at 3:21 PM,  <rado645-bg@yahoo.de> wrote:
> Dear Nick,
>
> thanks a lot! This was very helpful. Indeed, the event variable takes the 
value
> of 1 at the time of event and zero before that.
>
>
> I have just a quick question: how shall I proceed if I need to keep the year
> when the event has occurred and the previous year but drop any other preceding
> years?
>
> KR,
> Rado
>
>
>
> ----- Ursprüngliche Mail ----
> Von: Nick Cox <njcoxstata@gmail.com>
> An: statalist@hsphsun2.harvard.edu
> Gesendet: Mittwoch, den 20. Juli 2011, 21:49:22 Uhr
> Betreff: Re: st: on data transformation
>
> It is not clear what value -event- takes when it is not 1. I will suppose 0.
>
> bysort x year (event) : gen occurred = event[_N]
>
> spreads occurrences to all the weeks in the year in which they occurred.
>
> keep if occurred
>
> then -drops- entire years without events.
>
> Nick
>
> On Wed, Jul 20, 2011 at 2:41 PM,  <rado645-bg@yahoo.de> wrote:
>>
>> I would like to ask for help with data transformation. I have data on objects
>> x1, x2,x3  that are observed over time (weeks). I have variables var1 and 
var2
>> for each objects and also variable indicating the year of observation. In
>> addition, a variable "event" indicates the time period when an event has
>> occurred.
>>
>>
>> The columns of the panel data set look as follows:
>>
>> x  week      var1  var2 year event
>>
>> x1 2006w2 var1 var2 2006
>> x1 2006w3 var1 var2 2006
>> x1 2006w4 var1 var2 2006
>> x1 2007w7 var1 var2 2007
>> x1 2007w8 var1 var2 2007
>> x1 2007w9 var1 var2 2007
>> x1 2007w10 var1 var2 2007 1
>>
>> x2 2008w2 var1 var2 2008
>> x2 2008w3 var1 var2 2008
>> x2 2008w4 var1 var2 2008
>> x2 2009w9 var1 var2 2009
>> x2 2009w8 var1 var2 2009
>> x2 2009w9 var1 var2 2009
>> x2 2009w10 var1 var2 2009 1
>>
>> I have many variables x that differ in number of weeks and years. I need
>>however
>> to keep the year when the event has happened and dropped any previous years.
>> Given my data set, is this possible to be done in Stata?
>>

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