如何在PHP中找到值大于X的第一个数组元素？

Question

I have array with numeric values and I want to get key of first element which has value equal or greater than 5. Is there more elegant way than looping all elements in foreach ?

// "dirty" way
foreach ([0, 0, 4, 4, 5, 7] as $key => $value) {
    if ($value >= 5) {
        echo $key;
        break;
    }
}

Answer 1

The algorithm itself is perfectly fine, don't touch it.

That said, you could add some ribbons by writing a generic search function:

// find first key (from beginning of $a) for which the corresponding
// array element satisfies predicate $fn
function array_find(array $a, callable $fn)
{
    foreach ($a as $key => $value) {
        if ($fn($value, $key, $a)) {
            return $key;
        }
    }
    return false;
}

$key = array_find([0, 0, 4, 4, 5, 7], function($value) {
    return $value >= 5;
});

Now, although this is a more elegant approach, it's less efficient; there's a considerable overhead of calling the closure at each item. If performance is paramount, use what you have and run with it.

Answer 2

I have array with numeric values and I want to get key of first element which has value equal or greater than 5. Is there more elegant way than looping all elements in foreach ?

// "dirty" way
foreach ([0, 0, 4, 4, 5, 7] as $key => $value) {
    if ($value >= 5) {
        echo $key;
        break;
    }
}

Answer 3

Using array_search() can be efficient when seeking the earliest occurring match, but it is inappropriate in this case because it will not allow you to supply your required logic to the search.

Using functional iterators like array_map() and array_filter() are not ideal because they lack the ability to "short circuit" as soon as a match is made. In my own professional projects, I would not use a functional-style technique -- even on a relatively small data set -- because there is no valuable gain in doing so.

Considering the above, just use a classic loop with a condition in its body which breaks the loop as soon as a qualifying match occurs.

The $test variable is defined within a loop of test cases in my runnable demo links. To trial my code below, be sure to define $test as your needle before entering the loop.

Earliest key where array value is greater than or equal to the needle : ( Demo )

$array = [0, 0, 4, 4, 5, 7];

$foundKey = 'not found';
foreach ($array as $key => $value) {
    if ($value >= $test) {
        $foundKey = $key;
        break;
    }
}

Get key of highest value not greater than the needle : ( Demo )

$array = [0, 0, 4, 4, 5, 7];

$foundKey = 'not found';
foreach ($array as $key => $value) {
    if ($value > $test) {
        break;
    }
    $foundKey = $key;
}