R Language Code profiling proc.time()

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Example

At its simplest, proc.time() gives the total elapsed CPU time in seconds for the current process. Executing it in the console gives the following type of output:

proc.time()

#       user     system    elapsed 
#    284.507    120.397 515029.305 

This is particularly useful for benchmarking specific lines of code. For example:

t1 <- proc.time()
fibb <- function (n) {
    if (n < 3) {
        return(c(0,1)[n])
    } else {
        return(fibb(n - 2) + fibb(n -1))
    }
}
print("Time one")
print(proc.time() - t1)

t2 <- proc.time()
fibb(30)

print("Time two")
print(proc.time() - t2)

This gives the following output:

source('~/.active-rstudio-document')

# [1] "Time one"
#    user  system elapsed 
#       0       0       0 

# [1] "Time two"
#    user  system elapsed 
#   1.534   0.012   1.572 

system.time() is a wrapper for proc.time() that returns the elapsed time for a particular command/expression.

print(t1 <- system.time(replicate(1000,12^2)))
##  user  system elapsed 
## 0.000   0.000   0.002 

Note that the returned object, of class proc.time, is slightly more complicated than it appears on the surface:

str(t1)
## Class 'proc_time'  Named num [1:5] 0 0 0.002 0 0
##  ..- attr(*, "names")= chr [1:5] "user.self" "sys.self" "elapsed" "user.child" ...


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