Dynamically accessing multidimensional array value

Question

I'm trying to find (or create) a function. I have a multidimensional array:

$data_arr = [
    "a" => [
        "aa" => "abfoo",
        "ab" => [
            "aba" => "abafoo",
            "abb" => "abbfoo",
            "abc" => "abcfoo"
        ],
        "ac" => "acfoo"
    ],
    "b" => [
        "ba" => "bafoo",
        "bb" => "bbfoo",
        "bc" => "bcfoo"
    ],
    "c" => [
        "ca" => "cafoo",
        "cb" => "cbfoo",
        "cc" => "ccfoo"
    ]
];

And I want to access a value using a single-dimentional array, like this:

$data_arr_call = ["a", "ab", "abc"];

someFunction( $data_arr, $data_arr_call ); // should return "abcfoo"

This seems like there's probably already a function for this type of thing, I just don't know what to search for.

Right... it would pretty much take ['a', 'ab', 'abc'] and recognize that it means $data_arr['a']['ab']['abc'] — Phil Tune
– Phil Tune, Commented Mar 31, 2016 at 13:22

Phil Tune · Accepted Answer · 2016-03-31 14:54:57Z

9

Try this

function flatCall($data_arr, $data_arr_call){
    $current = $data_arr;
    foreach($data_arr_call as $key){
        $current = $current[$key];
    }

    return $current;
}

OP's Explanation:

The $current variable gets iteratively built up, like so:

flatCall($data_arr, ['a','ab','abc']);

1st iteration: $current = $data_arr['a'];
2nd iteration: $current = $data_arr['a']['ab'];
3rd iteration: $current = $data_arr['a']['ab']['abc'];

You could also do if ( isset($current) ) ... in each iteration to provide an error-check.

edited Mar 31, 2016 at 14:54

Phil Tune

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answered Mar 31, 2016 at 13:23

LibertyPaul

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9 Comments

Phil Tune Over a year ago

missing $key, where is it pulling that? Oh, I think you mean $data_arr_call as $key

LibertyPaul Over a year ago

@philtune yes, excactly

Rizier123 Over a year ago

While this code snippet may solve the question, including an explanation really helps to improve the quality of your post. Remember that you are answering the question for readers in the future, and those people might not know the reasons for your code suggestion. Please also try not to crowd your code with explanatory comments, this reduces the readability of both the code and the explanations!

Phil Tune Over a year ago

Yeah, I figured out why that works, but like @Rizier123 said, you should write up an explanation and I will accept this answer. Thanks.

LibertyPaul Over a year ago

@Rizier123 I'm sure that those 3 simple lines of code doesn't need any explanation. If you aren't agree with that you may do it yourself.

|

Casimir et Hippolyte · Accepted Answer · 2016-03-31 14:45:22Z

4

You can use this function that avoids the copy of the whole array (using references), is able to return a NULL value (using array_key_exists instead of isset), and that throws an exception when the path doesn't exist:

function getItem(&$array, $path) {
    $target = &$array;
    foreach($path as $key) {
        if (array_key_exists($key, $target))
            $target = &$target[$key];
        else throw new Exception('Undefined path: ["' . implode('","', $path) . '"]');
    }
    return $target;
}

demo:

$data = [
    "a" => [
        "aa" => "abfoo",
        "ab" => [
            "aba" => "abafoo",
            "abb" => NULL,
            "abc" => false
        ]
    ]
];

var_dump(getItem($data, ['a', 'ab', 'aba']));
# string(6) "abafoo"
var_dump(getItem($data, ['a', 'ab', 'abb']));
# NULL
var_dump(getItem($data, ['a', 'ab', 'abc']));
# bool(false)
try {
    getItem($data, ['a', 'ab', 'abe']);
} catch(Exception $e) {
    echo $e->getMessage();
}
# Undefined path: ["a","ab","abe"]

Note that this function can be improved, for example you can test if the parameters are arrays.

edited Mar 31, 2016 at 14:45

answered Mar 31, 2016 at 13:52

Casimir et Hippolyte

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1 Comment

Troy Niemeier Over a year ago

Yes! This is a much more responsible solution, passing a reference to the next iteration, instead of a copy of each step in the journey. Far less wasteful, and significantly more performant, it would seem.

Phil Tune · Accepted Answer · 2019-05-10 18:45:27Z

3

Wanted to post an even more elegant solution: array_reduce

    $data_arr = [
        "a" => [
            ...
            "ab" => [
                ...
                "abc" => "abcfoo"
            ],
            ...
        ],
        ...
    ];

    $result = array_reduce(["a", "ab", "abc"], function($a, $b) {
        return $a[$b];
    }, $data_arr);

    // returns "abcfoo"

I've been using Javascript's Array.reduce() a lot lately in updating some legacy code to ES6:

JS:
const data_obj = {...};
let result = ['a','ab','abc'].reduce((a, b) => a[b], data_obj);

answered May 10, 2019 at 18:45

Phil Tune

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Comments

Ali Farhoudi · Accepted Answer · 2016-03-31 13:38:19Z

0

You need a function like this:

function getValue($data_arr, $data_arr_call) {
    foreach ($data_arr_call as $index) {
        if (isset($data_arr[$index])) {
            $data_arr = $data_arr[$index];
        } else {
            return false;
        }
    }
    return $data_arr;
}

And use it like this:

$data_arr = [
    "a" => [
        "ab" => [
            "abc" => "abbfoo",
        ],
    ],
];
$data_arr_call = ["a", "ab", "abc"];
$value = getValue($data_arr, $data_arr_call);
if ($value) {
    // do your stuff
}

answered Mar 31, 2016 at 13:38

Ali Farhoudi

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