How to access N-th element of an array in PHP

问题:

I'm embarrassed to ask this and it's most likely a duplicate, but my google results are coming up short (im searching incorrectly I guess) and such a basic question is infuriating me.

I have an array containing values I don't know.

In java, to have a look at the 2nd entry, I would use something like

var = array[1]

I understand Php arrays are key-value pairs, but how can I simply look at the nth value in an array to see it's key-value pair, and even better, then access just the key / value?

回答1:

If your keys are numeric, then it works exactly the same:

$arr = ['one', 'two', 'three']; // equivalent to [0 => 'one', 1 => 'two', 2 => 'three']
echo $arr[1]; // two

If your keys are not numeric or not continuously numeric, it gets a bit trickier:

$arr = ['one', 'foo' => 'bar', 42 => 'baz'];

If you know the key you want:

echo $arr['foo']; // bar

However, if you only know the offset, you could try this:

$keys = array_keys($arr);
echo $arr[$keys[1]];

Or numerically reindex the array:

$values = array_values($arr);
echo $values[1];

Or slice it:

echo current(array_slice($arr, 1, 1));

Most likely you want to be looping through the array anyway though, that's typically what you do with arrays of unknown content. If the content is unknown, then it seems odd that you're interested in one particular offset anyway.

foreach ($arr as $key => $value) {
    echo "$key: $value", PHP_EOL;
}

回答2:

If you want to access the nth element without knowing the index, you can use next() n times to reach the nth element.

for($i = 0; $i<$n; $i++){
    $myVal = next();
}
echo $myVal;

There are other ways to access a specific element, already mentioned by @deceze.

回答3:

If you want to access every N-th element:

$n = 3;
foreach (array_keys($arr) as $i => $key) {
    if (($i+1) % $n) {
        continue;
    }

    $value = $arr[$key];
}