重置R中的循环变量 [英] Reset Loop Variable in R

问题描述

我正在for循环中遍历变量"i"，并希望根据if语句的结果将值重新分配给"i".下面的示例.

I am looping through a variable "i" in a for loop and want to reassign a value to "i" based on the outcome of an if statement. Example below.

for (i in 1:nrow(df)) {
     if (df[i, 5] > 4) {
          i <- 1
     } else {
          df[i, 5] <- df[1, 5] - 1
     }
}

如果我多次手动运行该脚本，该脚本将按预期工作，但是它似乎并未正确地重新分配我和/或在循环中将其注册.有想法吗?有什么建议吗?提前致谢！

The script works as expected if I manually run it multiple times, but it doesn't seem to be reassigning i correctly and/or registering it in the loop. Ideas? Suggestions? Thanks in advance!

推荐答案

在循环内更改 i 的值不会更改您在 1:nrow(df)中的位置.我认为这很好地说明了这一点:

Changing the value of i inside the loop won't change where you are in the 1:nrow(df). I think this illustrates nicely:

counter = 1
for (i in 1:3) {
    cat("counter ", counter, "\n")
    cat("i starts as ", i, "\n")
    i = 7
    cat("i is is set to ", i, "\n\n")
    counter = counter + 1
}
# counter  1 
# i starts as  1 
# i is is set to  7 
# 
# counter  2 
# i starts as  2 
# i is is set to  7 
# 
# counter  3 
# i starts as  3 
# i is is set to  7 

也许您应该使用 while 循环?我认为这是您要实现的目标，但是在您的问题中没有提供示例输入，解释或所需的输出，这只是一个猜测:

Maybe you should be using a while loop? I think this is what you are trying to achieve, but with no sample input, explanation, or desired output provided in your question, it's just a guess:

i <- 1
while (i <= nrow(df)) {
     if (df[i, 5] > 4) {
          i <- 1
     } else {
          df[i, 5] <- df[1, 5] - 1
          i <- i + 1
     }
}

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