CODEWITHSUNDEEP
rwhile-loopbooleanconditional-statements
Victor Nielsen
Victor Nielsen

Reputation: 493

How to continue a while loop while the condition is false in r?

I have this while loop:

while (abs(B-left)<INFSMALL | abs(B-right)<INFSMALL) {
...
}

I want it to run while the above condition is FALSE. Is there an easy way to do this?

Upvotes: 1

Views: 523

Answers (1)

r2evans
r2evans

Reputation: 160437

Use one of:

  1. Negate the entire conditional by wrapping it with !(.), as in

    while (!(abs(B-left) < INFSMALL || abs(B-right) < INFSMALL)) {
...
}

  2. Negate the components inside, and change from OR to AND:

    while (abs(B-left) >= INFSMALL && abs(B-right) >= INFSMALL) {
...
}

You should be using || instead of |, see Boolean operators && and ||. The flow-control functions if and while need the conditional to be length-1 exactly, not 0, no more than 1. While | will produce a vector of length 1 if all of the arguments are length 1, there are two reasons this is still a bad idea:

  1. Short-circuiting: in general, if the first (of multiple, chained) conditional suggests that the second (and beyond) conditional does not matter, than short-circuiting means it will not evaluate them. Without predefining aa, for instance, compare

    exists("aa") && aa > 0
# [1] FALSE
exists("aa") & aa > 0
# Error: object 'aa' not found

  2. Declarative code: the control-flow while must only take length-1, make sure you know this going in. It's perhaps a little bit of style, so more-so #1 above.

Upvotes: 1

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