Vectorization vs iterative loop

Loop

a<-runif(1000000, 1, 100)
b<-runif(1000000, 1, 100)
c.loop<-0
c.loop.time<-c(rep(0,10))

#loop method
for(i in 1:10){
  start.time <- Sys.time()
  for(j in 1:1000000){
    c.loop<-c.loop+a[j]*b[j]
  }
  c.loop.time[i]<-c(as.double(  Sys.time() - start.time))
}
#the 10 execution time
c.loop.time

##  [1] 1.0402119 1.0251732 0.9971929 1.0236001 1.0224719 1.0570061 1.0201309
##  [8] 1.0530169 1.0098500 1.0141699

print(paste0("The loop execution taks on average ",round(mean(c.loop.time),5) ," seconds."))

## [1] "The loop execution taks on average 1.02628 seconds."

Vectorization

c.vector<-0
c.vector.time<-c(rep(0,10))
#vectorization method
for(i in 1:10){
  start.time <- Sys.time()
  c.vector<-sum(a*b)
  c.vector.time[i]<-c(as.double(  Sys.time() - start.time))
}
c.vector.time

##  [1] 0.004498959 0.007035017 0.007002115 0.041497946 0.004499912
##  [6] 0.005006075 0.009495020 0.004502058 0.004501820 0.009001017

print(paste0("The vectorization execution takes on average  ",round(mean(c.vector.time),5) ," seconds."))

## [1] "The vectorization execution takes on average  0.0097 seconds."