Reset Loop Variable in R

Question

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
     }
}

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!

What do you mean by "doesn't seem to be reassigning correctly"? What is the behavior you are observing. It's easier to help you if you provide a [reproducible example](http://stackoverflow.com/questions/5963269/how-to-make-a-great-r-reproducible-example). Provide us some sample input and the desired output — MrFlick, Mar 23 '17 at 17:48
Just curious, but why would I get down votes? Assessed to be a bad question I assume? Perhaps lack of a reproducible example? — stevenjoe, Mar 23 '17 at 19:16
Just found this. My apologies for the question then although I am very grateful for the answer. "Downvoting implies that the question isn't well-researched." — stevenjoe, Mar 23 '17 at 19:19

score 2 · Accepted Answer · answered Mar 23 '17 at 17:55

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

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
     }
}

Ahhhh... okay. If that is the case, I think that would be the problem. I appreciate the insight and provision of the `while` format. I will attempt a revision with `while`. Thanks for your help! — stevenjoe, Mar 23 '17 at 19:13

Reset Loop Variable in R

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