R help - Jul 2011 - sum part of a vector

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.

I'm trying as follows but I get really weird results. One thing is that it
keeps counting 0's as 1.

for (i in levels(mydat$state)) {
mydat[mydat$state==i, ]$cum.news<-sapply(mydat[mydat$state==i, ]$news,
function(x) sum(1:x))
}

I can sort of get the same sapply function to do what I want when working on a
test string
test<-1:10
sapply(test, function(x) sum(1:x))

Any thoughts?
Simon Kiss
*********************************
Simon J. Kiss, PhD
Assistant Professor, Wilfrid Laurier University
73 George Street
Brantford, Ontario, Canada
N3T 2C9
Cell: +1 905 746 7606

Hi Simon,

Is this what you want?

mydat$cum.news<-unlist(tapply(mydat$news,mydat$state,FUN=cumsum))

Weidong Gu

On Sat, Jul 23, 2011 at 7:11 AM, Simon Kiss <sjkiss at gmail.com>
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.
>
> I'm trying as follows but I get really weird results. One thing is that
it keeps counting 0's as 1.
>
> for (i in levels(mydat$state)) {
> mydat[mydat$state==i, ]$cum.news<-sapply(mydat[mydat$state==i, ]$news,
function(x) sum(1:x))
> }
>
> I can sort of get the same sapply function to do what I want when working
on a test string
> test<-1:10
> sapply(test, function(x) sum(1:x))
>
> Any thoughts?
> Simon Kiss
> *********************************
> Simon J. Kiss, PhD
> Assistant Professor, Wilfrid Laurier University
> 73 George Street
> Brantford, Ontario, Canada
> N3T 2C9
> Cell: +1 905 746 7606
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>

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
Solbjerg Plads 3, 2000 Frederiksberg, Denmark
Phone: (+45)38153501
Email: pd.mes at cbs.dk  Priv: PDalgd at gmail.com
"D?den skal tape!" --- Nordahl Grieg