前言

最近寫了一個小程式，要測試它的執行時間，因此特地看了一下R如何記錄執行時間。

正文

proc.time {base} R Documentation
Running Time of R

Description

proc.time determines how much real and CPU time (in seconds) the currently running R process has already taken.

Usage

proc.time()
Details

proc.time returns five elements for backwards compatibility, but its print method prints a named vector of length 3. The first two entries are the total user and system CPU times of the current R process and any child processes on which it has waited, and the third entry is the ‘real’ elapsed time since the process was started.

Value

An object of class “proc_time” which is a numeric vector of length 5, containing the user, system, and total elapsed times for the currently running R process, and the cumulative sum of user and system times of any child processes spawned by it on which it has waited. (The print method uses the summary method to combine the child times with those of the main process.)

The definition of ‘user’ and ‘system’ times is from your OS. Typically it is something like

The ‘user time’ is the CPU time charged for the execution of user instructions of the calling process. The ‘system time’ is the CPU time charged for execution by the system on behalf of the calling process.

Times of child processes are not available on Windows and will always be given as NA.

The resolution of the times will be system-specific and on Unix-alikes times are rounded down to milliseconds. On modern systems they will be that accurate, but on older systems they might be accurate to 1/100 or 1/60 sec. They are typically available to 10ms on Windows.

Examples

## a way to time an R expression: system.time is preferred
ptm <- proc.time()
for (i in 1:50) mad(stats::runif(500))
proc.time() - ptm