限制函数在 R for 循环中处理的时间 [英] Limiting the time that a function processes in an R for loop

问题描述

我想应用一个函数(本解释中的foo")将数据向量转换为另一个值.该函数以数据为输入，需要向网页提交表单.有时，这进行得很快，而有时，可能会持续很长时间.我想以跳过花费太长时间的项目的方式运行 for 循环(或等效的 apply 函数).我尝试使用以下方法限制循环运行的时间，然后再跳到接下来的 5 秒:

I want to apply a function ("foo" for this explanation) to tranform a vector of data into another value. This function takes the data as an input, and needs submit forms to webpages. Sometimes, this goes quickly, and other times, it can a long time. I would like to run the for loop (or equivalent apply function) in a way that skips over the items that take too long. I have tried to limit the time the loop runs before skipping to the next to 5 seconds using the following:

pb <- txtProgressBar(min = 1, max = 100, style = 3)
storage <- matrix(nrow = sample.length, ncol = 2)

for(i in 1:100){  
     s <- Sys.time()  
     storage[i,] <- try(foo(data.vec[i]), TRUE)  
     if (Sys.time() - s >5) {next}  
     # update progress bar  
     setTxtProgressBar(pb, i)  
}  
close(pb)  

我想我一定不明白如何在 for 循环中应用下一个"条件.已经搜索找到更清晰的解释，但在这里没有任何运气.

I think that I must not be understanding how to apply the 'next' condition in a for loop. have searched to find a clearer explanation, but not getting any luck here.

推荐答案

withTimeout() 来自包 R.utils，与 tryCatch()<一致/code>，可能会提供更简洁的解决方案.

withTimeout() from package R.utils, in concert with tryCatch(), might provide a cleaner solution.

例如:

require(R.utils)

for(i in 1:5) {
    tryCatch(
        expr = {
            withTimeout({Sys.sleep(i); cat(i, "
")}, 
                         timeout = 3.1)
            }, 
        TimeoutException = function(ex) cat("Timeout. Skipping.
")
    )
}

# 1 
# 2 
# 3 
# Timeout. Skipping.
# Timeout. Skipping.

在上面的人工例子中:

• withTimeout() 的第一个参数包含要在每个循环中计算的代码.

• The first argument to withTimeout() contains the code to be evaluated within each loop.

withTimeout() 的 timeout 参数以秒为单位设置时间限制.

The timeout argument to withTimeout() sets the time limit in seconds.

tryCatch() 的 TimeoutException 参数采用一个函数，该函数将在循环迭代超时时执行.

The TimeoutException argument to tryCatch() takes a function that is to be executed when an iteration of the loop is timed out.

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