我想在特定时间运行R代码

Question

我想在我需要的特定时间运行R代码。 并且在处理完成后，我想终止R会话。

如果代码是如下，

tm<-Sys.time() 
write.table(tm,file='OUT.TXT', sep='\t'); 
quit(save = "no") 

我应该怎么做才能运行在“2012-04-18十七时25分40秒”这个代码。 我需要你的帮助。提前致谢。

Answer 1

在Linux下最容易使用Windows的Task Scheduler或cron job。在那里你可以指定一个应该在你指定的特定时间运行的命令或程序。我肯定会不建议喜欢的R脚本：

time_to_run = as.POSIXct("2012-04-18 17:25:40") 
while(TRUE) { 
    Sys.sleep(1) 
    if(Sys.time == time_to_run) { 
    ## run some code 
    } 
} 

Answer 2

如果不知为何，你不能使用cron作业服务，并有R内安排，下列R-代码演示如何等待特定的时间量，从而在预先指定的目标时间执行。

stop.date.time.1 <- as.POSIXct("2012-12-20 13:45:00 EST") # time of last afternoon execution. 
stop.date.time.2 <- as.POSIXct("2012-12-20 7:45:00 EST") # time of last morning execution. 
NOW <- Sys.time()          # the current time 
lapse.time <- 24 * 60 * 60    # A day's worth of time in Seconds 
all.exec.times.1 <- seq(stop.date.time.1, NOW, -lapse.time) # all of afternoon execution times. 
all.exec.times.2 <- seq(stop.date.time.2, NOW, -lapse.time) # all of morning execution times. 
all.exec.times <- sort(c(all.exec.times.1, all.exec.times.2)) # combine all times and sort from recent to future 
cat("To execute your code at the following times:\n"); print(all.exec.times) 

for (i in seq(length(all.exec.times))) { # for each target time in the sequence 
    ## How long do I have to wait for the next execution from Now. 
    wait.time <- difftime(Sys.time(), all.exec.times[i], units="secs") # calc difference in seconds. 
    cat("Waiting for", wait.time, "seconds before next execution\n") 
    if (wait.time > 0) { 
    Sys.sleep(wait.time) # Wait from Now until the target time arrives (for "wait.time" seconds) 
    { 
     ## Put your execution code or function call here 
    } 
    } 
}