----- Original Message -----
From: "Jitian Sheu" <[email protected]>
To: <[email protected]>
Sent: Wednesday, September 10, 2003 10:01 AM
Subject: st: Creating variables = sum(last year)
> Dear Listers:
> I am not sure my subject title is correct
>
> My question is as following:
>
> Suppose I have data as following:
>
> obs id date vol X
> 1 1 01 jan 1995 a -
> 2 1 28 feb 1995 b a
> 3 1 31 oct 1996 c a
> 4 1 25 dec 1996 d d
> 5 1 29 dec 1996 e c+d
> 6 1 15 nov 1997 f c+d
> 7 2 01 jan 1994 g -
> 8 2 10 jan 1994 h g
> 9 2 25 jan 1994 i g+h
> 10 2 3 feb 1994 j g+h+i
> 11 2 28 feb 1994 k g+h+i+j
> 12 2 01 jan 1995 l g+h+i+j+k
> 13 2 11 jan 1995 m g+h+i+j+k+l
>
>
> What I want is a new varialbe, say call X
> Where X is the summation of "VOL" for the same ID, but, the summation only
> count for one year behind the date of underlying observation.
>
> For example, take a look for observation #5.
> This observation has date ="29 Dec 1996" (for ID=1)
> The value of this new variable = all "VOL" occured between "29 Dec 1995" -
> "28 Dec 1996".
> In this case the value is "c+d"
>
> Take another example.
> Let's see the observation #10.
> This observation has date= "3 Feb 1994"
> I want the X to be the summation of all VOL occured between "3 Feb 1993" to
> "2 Feb 1994", ===> =g+h+i
>
>
> Does anyone have suggestion?
>
>
> Thank you very much
>
>
> JT
>
No suggestions, but a question about variable x.
If x is the the sum of last year's vol then should not x = . for observation 3,
since the time span from observation 2 to 3 is one year eight months;
observation 6 would be the sum of observations 4 and 5 and obersvation 12 would
be the sum of observations 9 - 11. So, should the final data set look something
like this:
obs id date vol X
1 1 01 jan 1995 a -
2 1 28 feb 1995 b a
3 1 31 oct 1996 c -
4 1 25 dec 1996 d c
5 1 29 dec 1996 e c+d
6 1 15 nov 1997 f d+e
7 2 01 jan 1994 g -
8 2 10 jan 1994 h g
9 2 25 jan 1994 i g+h
10 2 3 feb 1994 j g+h+i
11 2 28 feb 1994 k g+h+i+j
12 2 01 jan 1995 l g+h+i+j+k
13 2 11 jan 1995 m i+j+k+l
Scott
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