<br />
> tmp=rnorm(400)<br />
> area=numeric(40)<br />
> system.time(for(j in 1:1e4)for ( n in 1:40 ){area[n]=sum(tmp[((n-1)*10+1):(n*10)])})<br />
user system elapsed <br />
6.68 0.00 7.56 <br />
> system.time(for(i in 1:1e4)colSums(matrix(tmp,nr=10)))<br />
user system elapsed <br />
0.88 0.00 1.03 <br />
> system.time(for(i in 1:1e4)tapply(tmp, rep(1:40, each=10), sum))<br />
user system elapsed <br />
19.42 0.01 22.95 <br />