[R] sum part of a vector

[peter dalgaard]

On Jul 23, 2011, at 13:11 , Simon Kiss wrote:

> Dear colleagues, I have a data set that looks roughly like this;
> mydat<-data.frame(state=c(rep("Alabama", 5), rep("Delaware", 5), rep("California", 5)), news=runif(15, min=0, max=8), cum.news=rep(0, 15))
> 
> For each state, I'd like to cumulatively sum the value of "news" and make that put that value in cum.news.

Like this?

> mydat <- within(mydat, cum.news <- ave(news, state, FUN=cumsum))
> mydat
        state      news  cum.news
1     Alabama 7.9914863  7.991486
2     Alabama 7.3751514 15.366638
3     Alabama 3.4894295 18.856067
4     Alabama 3.1543811 22.010448
5     Alabama 7.9720879 29.982536
6    Delaware 2.3904745  2.390475
7    Delaware 5.5532841  7.943759
8    Delaware 5.4182249 13.361984
9    Delaware 4.6554645 18.017448
10   Delaware 3.1289714 21.146419
11 California 7.9450424  7.945042
12 California 2.0142029  9.959245
13 California 7.9735398 17.932785
14 California 1.0972878 19.030073
15 California 0.7215365 19.751609


-- 
Peter Dalgaard, Professor,
Center for Statistics, Copenhagen Business School
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Email: pd.mes at cbs.dk  Priv: PDalgd at gmail.com
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