normalizing prizes to a specific year - how to?

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Dear list

I have a large data frame with house prices. Prices have been  
converted
to price per m2, to be able to compare. Prices are spread over  
almost 10
years, each price is tagged with the year it relates to.

I would like to 'normalize' all the prices to, eg. 2010 prices.

The data frame looks like this

head(dafP)
Y P

1 2004 11199.60

2 2005 15310.10

3 2005 19491.50

4 2005 18656.70

5 2005 16092.00

6 2005 9929.08

Y is Year and P is price (in Danish Kroner) per m2

I looked in some old scripts and have written this:

dafP$Yav <- ave(dafP$P,dafP$Y,FUN=mean) # Yav. Prices Weight per Year,
i.e. Yearly mean

dafP$Pno <- dafP$P * (mean(dafP$P)/dafP$Yav) # Prize Normalized by  
Year

Can any one comment on this:

   *

     This code only normalizes so all year get the same mean. How  
would
     I go about 'normalizing' to a specific year, eg. 2010?
? tapply

Maybe something like:

mn2010 <- head(dafP[which(dafP$Y==2010), "Yav"], 1) # get just first  
2010 value
with(dafP,   tapply(P, Y, scale, center=mn2010) )

aggregate can be used with scale and may be better in some instances.  
Testing is not done here because you failed to provide a useful example.
David

>
> Best Regards
>
> Martin
>
>
> -- 
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David Winsemius, MD
West Hartford, CT