# st: Re: Creating variables = sum(last year)

 From "Scott Merryman" To Subject st: Re: Creating variables = sum(last year) Date Wed, 10 Sep 2003 22:21:09 -0500

```----- Original Message -----
From: "Jitian Sheu" <jtsheu@bu.edu>
To: <statalist@hsphsun2.harvard.edu>
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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