# File name: loop_for_1.r

my.loop <- 20
m.dim <- list(nrow = 200000, ncol = 10)
m <- matrix(1, nrow = m.dim$nrow, ncol = m.dim$ncol)
ret <- 0

start <- Sys.time()
for(k in 1 : my.loop){
  for (i in 1 : m.dim$nrow){
    for (j in 1 : m.dim$ncol){
      ret <- ret + m[i, j]
    }
  }
}
Sys.time() - start

# File name: loop_for_2.r

my.loop <- 20
m.dim <- list(nrow = 200000, ncol = 10)
m <- matrix(1, nrow = m.dim$nrow, ncol = m.dim$ncol)
ret <- 0

start <- Sys.time()
for(k in 1 : my.loop){
  for (j in 1 : m.dim$ncol){
    for (i in 1 : m.dim$nrow){
      ret <- ret + m[i, j]
    }
  }
}
Sys.time() - start

# File name: loop_apply.r

my.loop <- 20
m.dim <- list(nrow = 200000, ncol = 10)
m <- matrix(1, nrow = m.dim$nrow, ncol = m.dim$ncol)
ret <- 0

start <- Sys.time()
for(k in 1 : my.loop){
  ret <- ret + sum(apply(m, 1, sum))
}
Sys.time() - start

# File name: loop_rowSums.r

my.loop <- 20
m.dim <- list(nrow = 200000, ncol = 10)
m <- matrix(1, nrow = m.dim$nrow, ncol = m.dim$ncol)
ret <- 0

start <- Sys.time()
for(k in 1 : my.loop){
  ret <- ret + sum(rowSums(m))
}
Sys.time() - start

c File name: lood_dyn.f
c For dynamical load compile by g77.
c SHELL> g77 -c loop_dyn.f ; g77 -shared -o loop_dyn.so loop_dyn.o

      subroutine dynsum(nrow, ncol, m, ret)
        integer i, j, nrow, ncol
        real*8 m(nrow, ncol), ret

        ret = 0
        do j = 1, ncol
          do i = 1, nrow
            ret = ret + m(i, j) 
          end do
        end do

        return
      end

c Output is a shared library "loop_dyn.so" can called by R.

# File name: loop_dyn.r

dyn.load("loop_dyn.so")
# For Windows will like this
# dyn.load("C:/Windows/Desktop/loop_dyn.dll")

my.loop <- 20
m.dim <- list(nrow = 200000, ncol = 10)
m <- matrix(1, nrow = m.dim$nrow, ncol = m.dim$ncol)
ret <- 0

dynsum.f <- function(m) {
  ret <- .Fortran("dynsum", nrow = nrow(m), ncol = ncol(m),
           m = as.double(m), ret = as.double(m))
  ret$ret
}

start <- Sys.time()
for(k in 1 : my.loop){
  ret <- ret + dynsum.f(m)
}
Sys.time() - start

dyn.unload("loop_dyn.so")
# For Windows will like this
# dyn.unload("C:/Windows/Desktop/loop_dyn.dll")