突破R中的嵌套循环 [英] Breaking out of nested loops in R

问题描述

非常简单的示例代码(仅用于演示，根本不使用):

Very simple example code (only for demonstration, no use at all):

repeat {
  while (1 > 0) {
    for (i in seq(1, 100)) {
      break # usually tied to a condition
    }
    break
  }
  break
}
print("finished")

我想从多个循环中脱颖而出，而不必在每个循环中分别使用break. 根据关于python的类似问题，将我的循环到一个函数中似乎是一种可能的解决方案，即使用return()打破该函数中的每个循环:

I want to break out from multiple loops without using break in each loop separately. According to a similar question regarding python, wrapping my loops into a function seems to be a possible solution, i.e. using return() to break out of every loop in the function:

nestedLoop <- function() {
  repeat {
    while (1 > 0) {
      for (i in seq(1, 100)) {
        return()
      }
    }
  }
}

nestedLoop()
print("finished")

R中还有其他可用的方法吗?也许像标记循环之类的，然后指定要中断的循环(例如在Java中)?

Are there other methods available in R? Maybe something like labeling loops and then specifying which loop to break (like in Java) ?

推荐答案

使用显式标志，并有条件地打破这些标志的循环，可以提供更大的灵活性.示例:

Using explicit flags, and breaking out of loops conditionally on those flags can give one more flexibility. Example:

stop = FALSE
for (i in c(1,2,3,4)){
    for (j in c(7,8,9)){
        print(i)
        print(j)
        if (i==3){
            stop = TRUE # Fire the flag, and break the inner loop
            break
        }
        }
    if (stop){break} # Break the outer loop when the flag is fired
    }

当i=3时，上面的代码将打破两个嵌套循环.当最后一行(if (stop){break})被注释掉时，只有内部循环在i=3处断开，但外部循环继续运行，即实际上跳过了i=3的情况.这种结构易于使用，并且可以根据需要灵活地进行.

The above code will break the two nested loops when i=3. When the last line (if (stop){break}) is commented out, then only the inner loop gets broken at i=3, but the outer loop keeps running, i.e. it practically skips the cases of i=3. This structure is easy to play around with, and is as flexible as one may need.

这篇关于突破R中的嵌套循环的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！