R: Make this loop faster using sapply -

i'm new in r , i'm trying figure out how make function faster using sapply, help?

x <- c(0.0, 1.0, 2.0, 3.0, 4.0, 5.7) y <- c(10.0, 7.0, 5.5, 4.5, 3.2, na) z <- c(as.data.frame(cbind(x,y))   vcub=function(y, x, z)  {     vol<-vector()     for(i in 1:dim(z)[1]){         if(is.na(y[i]))         {           vol[i]<-(((pi*y[i-1]^2)/40000)/3)*(x[i]-x[i-1])         }else{           vol[i]<-(((pi*y[i-1]^2) + (pi*y[i]^2))/80000)*(x[i]-x[i-1])         }     }     return(as.data.frame(vol)) }     

you can vectorize code replacing if , else statements in loop ifelse statement , using vectorized arithmetic in r:

data.frame(vol=ifelse(is.na(y), pi*c(na, head(y, -1)^2)/120000*c(na, diff(x)),                       pi*(y^2 + c(na, head(y, -1)^2))/80000*c(na, diff(x)))) #            vol # 1           na # 2 0.0058512163 # 3 0.0031121402 # 4 0.0019831304 # 5 0.0011973395 # 6 0.0004557404 

in general, it's easy vectorize computation when can compute i^th index of result without using of previous indices computed. since formula vol[i] didn't depend on of previous vol values, can use basic arithmetic operators.