如何跟踪变量值是否在同一个php while循环中多次使用

Question

I found this snippet in a different question and answer, and it detects if a variable value is the same as the variable value in the previous loop.

$prevValue = NULL;
while(condition) {
 if ($curValue == $prevValue) {
  //do stuff
 }
 $prevValue = $curValue;
}

However what I want to do is to check if a variable value has been used before in the loop, but anywhere in the loop, so if the value happened 1 or 2 or 10 loops ago I want it to tell me if the variable value has come through the loop before.

Answer 1

Use an array to store each value and then check if the current value is in the array:

$prevValues = array();
while(/*condition*/) {
    if (in_array($curValue, $prevValues)) {
        //do stuff
    }
    $prevValues[] = $curValue;
}

As Marc B points out in a comment, you can do it this way as well. It might be marginally faster but I haven't tested it:

while(/*condition*/) {
    if (isset($prevValues[$curValue])) {
        //do stuff
    }
    $prevValues[$curValue] = 1;  //set to whatever
}