Add certain rows in a column that satisfy condition in R? -

i using r , want add values within column if rows satisfy condition. if have data frame data below:

 team mp win  atl  14 .4  atl  25 .4  atl  14 .4  bos  14 .55  bos  20  .55  bos  9  .55 

how store values of mp atl (14+25+14 = 53)and bos (14+20+9=43)?

edit: if want add new variable multiplies win mp/sums (where sums sum of mp each team). atl variables, want values .4*14/53 , .4*25/53, , bos want .55*14/43, .55*20/43, .55*9/43

i think produce you're looking for:

edit

in light of akrun's excellent answer, here's more compact solution:

dat$cumsums <- ave(dat$mp, dat$team, fun=sum) dat$newvar <- with(dat, win * (mp/cumsums)) 

previous solution

cumsums <- by(data = dat$mp, indices = dat$team, fun = sum) cumsums.df <- data.frame(team = names(cumsums), cumsums = as.numeric(cumsums)) dat <- merge(x=dat, y=cumsums.df, = "team") dat$newvar <- with(dat, win * (mp/cumsums)) 

results

dat   team mp  win cumsums    newvar 1  atl 14 0.40      53 0.1056604 2  atl 25 0.40      53 0.1886792 3  atl 14 0.40      53 0.1056604 4  bos 14 0.55      43 0.1790698 5  bos 20 0.55      43 0.2558140 6  bos  9 0.55      43 0.1151163 

data

dat <- read.csv(text="team,mp,win atl,14,.4 atl,25,.4 atl,14,.4 bos,14,.55 bos,20,.55 bos,9,.55")