Hi:
Try this from package plyr:
library(plyr)
# function to compute sum of squares
f <- function(df) with(df, sum((tapply(value, type, sum)/sum(value))^2))
# apply it to each type of food:
ddply(data, .(food), conc = f(data))
food type value market_con
1 drink water 5 0.5987654
2 drink soda 7 0.5987654
3 drink soda 6 0.5987654
4 fruit apple 2 0.7222222
5 fruit apple 3 0.7222222
6 fruit orange 1 0.7222222
HTH,
Dennis
On Wed, Aug 11, 2010 at 3:40 PM, Yi <liuyi.fe...@gmail.com> wrote:
> Thank you for reminding me.
>
> ######
> food=c('fruit','fruit','fruit','drink','drink','drink')
> type=c('apple','apple','orange','water','soda','soda')
> value=c(2,3,1,5,7,6)
> data=data.frame(food,type,value)
> share=c((2+3)/(2+3+1),5/6,1/6,5/(5+7+6),13/18,13/18)
> market_con=c(rep(0.8333333^2+0.1666667^2,3),rep(0.2777778^2+0.7222222^2,3))
> data$market_con=market_con
> ######
>
> Share= sum of value for specific type for some food / sum of value for all
> types for some food
>
> concentration= sum of square of share
>
> For food 1, fruit, for apple ,there are two rows, value =2 and 3; for
> oranget, value =1.
>
> share_apple=(2+3)/(2+3+1)=5/6 ## It is the same for the two rows
> share_organge=1/6
>
> concentration_fruit= share_apple^2+sjare_orange^2=(5/6)^2+(1/6)^2
>
> Hope this makes it easier to understand.
>
> Thanks
>
> Yi
>
> On Wed, Aug 11, 2010 at 3:33 PM, Wu Gong <w...@mtmail.mtsu.edu> wrote:
>
> >
> > Hi Yi,
> >
> > It would be helpful for others to provide a solution if you give your
> > formulas that calculating the value of share and concentration.
> >
> > ?apply will helps.
> >
> > Regards,
> >
> > Wu
> >
> >
> >
> > -----
> > A R learner.
> > --
> > View this message in context:
> >
> http://r.789695.n4.nabble.com/How-to-calculate-the-concentration-tp2321888p2321966.html
> > Sent from the R help mailing list archive at Nabble.com.
> >
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> >
>
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