Date:         Thu, 13 Jan 2000 19:11:44 +0100
Reply-To:     "Christian F.G. Schendera" <schendera@NIKOCITY.DE>
Sender:       "SAS(r) Discussion" <SAS-L@LISTSERV.UGA.EDU>
From:         "Christian F.G. Schendera" <schendera@NIKOCITY.DE>
Subject:      Q: lag function
Comments: To: SASL <SAS-L@UGA.CC.UGA.EDU>
Content-Type: text/plain; charset="iso-8859-1"

I have the following lag function code..........

data PCTVLF2 ;
set PCTVLF1 ;
by YEARPAIR BIRDTYPE METHOD ;
a=lag(PCTDIFF) ;
if first.METHOD then PCTDEV=100 ;
else PCTDEV =(PCTDIFF/a*100)-100 ;
put PCTDEV = ;
run ;


.........and want to have the output look like this:

BIRDTYPE  METHOD YEARPAIRs
                                         92/93
93/94.............            94/95
Blackbird            L     130.303 (PCTDIFF +30.303 to start value 100%)
xyz (130.303+/-PCTDIFF)      abc (xyz+/-PCTDIFF).............
Blackbird            P                   ................
Finch                   L     64.865 (100%-PCTDIFF 35.135) xyz
(130.303+/-PCTDIFF)
Finch                   P......
My general aim is to have an annual data development expressed in
percentages. The first yearpair is related to 100% to get some standardized
beginning. Then all other differences are percentage calculated from the
obtained results. My LAG code is very close to this output but there seems
to be a little flaw about the starting value. I cannot get it started with
the right YEARPAIR.
Help appreciated, Chris

*******************example PCTVLF1 dataset structure*****************

note: Dataset contains two data  rows per BIRDTYPE and YEARPAIR: Methods L
and P. Yearpair range from 92/93 (for some birdtypes later) to yearpair
97/98. QJ1 and QJ2 are percentage values for years1 and 2. PDIFF stands for
the difference between QJ1 and QJ2 as asolute amount. PCTDIFF expresses this
absolute amount difference as percentage quotient related to QJ1.
           OBS    YEARPAIR    YEAR1    YEAR2    BIRDTYPE
METHOD       QJ1     QJ2    PDIFF     PCTDIFF

             1     92/93       1992     1993    Blackbird        L
16.5    21.5      5.0      30.303
             2     92/93       1992     1993    Finch     L            18.5
12.0     -6.5     -35.135
             3     92/93       1992     1993    Eagle     L             0.5
1.5      1.0     200.000
             4     92/93       1992     1993    Eagle      L
4.5     5.5      1.0      22.222
             5     92/93       1992     1993    Crow       L            18.5
28.5     10.0      54.054
             6     92/93       1992     1993    Chicken     L
1.5     0.5     -1.0     -66.667
             7     92/93       1992     1993    Whale ;-) L             1.0
1.0      0.0       0.000
             8     92/93       1992     1993    Sparrow    L             0.5
0.5      0.0       0.000...................