Using empty string as key in associative array

Question

I need to select and group some items according to some values and it's easy using an associative multidimensional array:

$Groups = array(
    "Value1" = array("Item1", "Item3"),
    "Value2" = array("Item2", "Item4")
    );

But some items hasn't the value so my array will be something like:

$Groups = array(
    "Value1" = array("Item1", "Item3"),
    "Value2" = array("Item2", "Item4")
    "" = array("Item5", "Item6")
    );

I've tested it (also in a foreach loop) and all seems to work fine but I'm pretty new to php and I'm worried that using an empty key could give me unexpected issues.

Is there any problem in using associative array with empty key?
Is it a bad practice?
If so, how could I reach my goal?

Where do you get the array from? What are you using it for? If it's good or bad depends on the use case. — M. Eriksson
– M. Eriksson, Commented Mar 1, 2018 at 21:32
@Litty I mean an equivalent of the second array. Anyway I've got answers — genespos
– genespos, Commented Mar 1, 2018 at 21:34
'Some items', implies you may have more than one empty string as a key, which of course will result in clobbering. Perhaps you should generate unique ids for these. — Progrock
– Progrock, Commented Mar 1, 2018 at 22:10
You also should the double arrow operator => for key value pairs when defining arrays. — Progrock
– Progrock, Commented Mar 1, 2018 at 22:14

Lightness Races in Orbit · Accepted Answer · 2018-03-01 21:36:39Z

5

There's no such thing as an empty key. The key can be an empty string, but you can still access it always at $groups[""].

The useful thing of associative arrays is the association, so whether it makes sense to have an empty string as an array key is up to how you associate that key to the value.

edited Mar 1, 2018 at 21:36

Lightness Races in Orbit

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answered Mar 1, 2018 at 21:32

Devon Bessemer

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3 Comments

genespos Over a year ago

Yes it's not empty but empty string! I'll update the question title

Devon Bessemer Over a year ago

@LightnessRacesinOrbit An empty string still is has a way to be referenced. You can't do $array = [ => "value" ] but $array = [ "" => "value"] is fine.

Lightness Races in Orbit Over a year ago

@Devon: Yeah I'd misread genespos comment (mainly because the former example makes so little sense it hadn't even entered my mind!)

Ivan Kalita · Accepted Answer · 2018-03-01 21:40:56Z

2

You can use an empty string as a key, but be careful, cause null value will be converted to empty string:

<?php

$a = ['' => 1];

echo $a[''];
// prints 1

echo $a[null];
// also prints 1

I think, it's better to declare some "no value" constant (which actually has a value) and use it as an array key:

<?php

define('NO_VALUE_KEY', 'the_key_without_value');

$a = [NO_VALUE_KEY => 1];

edited Mar 1, 2018 at 21:40

answered Mar 1, 2018 at 21:35

Ivan Kalita

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