searching multidimensional associative arrays

bagus

If I have an array that dumps as below, how can I get the fieldname where parameterId = 177. Ideally with out a foreach. Thanks,

[0]=>
array(2) {
["parameterId"]=>
string(3) "169"
["fieldName"]=>
string(9) "nothing"
}
[1]=>
array(2) {
["parameterId"]=>
string(3) "177"
["fieldName"]=>
string(17) "something"
[2]=>
array(2) {
["parameterId"]=>
string(3) "174"
["fieldName"]=>
string(9) "gimme"
}

devinemke

why don't you want to use foreach?

$array = array(
array('parameterId' => '169', 'fieldName' => 'nothing'),
array('parameterId' => '177', 'fieldName' => 'something'),
array('parameterId' => '174', 'fieldName' => 'gimme')
);

foreach ($array as $key => $value)
{
	if ($value['parameterId'] == '177') {echo $value['fieldName'];}
}

NogDog

You could optimize it a bit by breaking out of the loop once you find a match:

$fieldname = null;
foreach($array as $value)
{
   if($value['parameterid'] == 177)
   {
      $fieldname = $value['fieldname'];
      break;
   }
}

devinemke

NogDog;10891632 wrote:
You could optimize it a bit by breaking out of the loop once you find a match:

...however there could be multiple matches

NogDog

devinemke;10891633 wrote:
...however there could be multiple matches

Yes, if (a) there could be multiple matches and (b) the requirement is to get all such matches, then you would not want to break the loop. I had assumed from the wording of the original post that only one match was wanted or expected; but as always, assumptions can be dangerous. 😉

Weedpacket

But if you do want to avoid foreach for some unspecified reason, [man]array_map[/man] and [man]array_filter[/man] can be used to traverse the array instead.

bagus

Weedpacket;10891718 wrote:
But if you do want to avoid foreach for some unspecified reason, [man]array_map[/man] and [man]array_filter[/man] can be used to traverse the array instead.

Thanks for the lead. But how would this work? How would my function know to look for the value fieldName where the parameterId is 177?

Using devinmke's definition of my array as $array, it seems as if array_filter must call a function with only one parameter and that would be my $array, but really I need a second parameter that is '177'.

Can you pass a parameter in with the call back like this or something:

$fieldNameFor177 = array_filter($array, "getFieldName", 177);

Thanks,

Bagus

Weedpacket

If you don't know in advance that the parameterID should be 177 then it gets messier; use [man]create_function[/man] and construct the source code of the function in a string, inserting the variable containing "177" in the appropriate place (you're lucky it's only an integer and not something more complicated).

That's the cleanest way of doing it: alternatives involve global variables or additional private fields (if this is in an object). It's a glaring problem that has been fixed in PHP v5.3, where you'd just write

// Where $n=177;
array_filter($array, function($elt)use($n){return $elt['parameterId']==$n;});

But until then, the filter function would have to be created as source code with the value of $n concatenated:

create_function('$elt', 'return $elt["parameterId"]=='.$n.';')

bagus

That worked great. I'll say that the mysterious reason behind my not wanting to use a foreach has something to do with me occasionally seeing a memory error that brings down my site and that points to the existing foreach code which was inside a smarty template.

So....

I'm not sure this will be more efficient, and I have now read about there being some issues with memory leaks and the create_function(). So whatever caused my memory leak before may do the same thing again. I'll be watching. At least there's a few less lines of code. (tho a few more comments)

I am not completely sure with this notation:

$elt['parameterId']==$n;

I assume that is actually somehow doing a foreach and only returning when it is true. Is that right?

I ended up with code that looked like this:

$array = array(
array('parameterId' => '169', 'fieldName' => 'nothing'),
array('parameterId' => '177', 'fieldName' => 'something'),
array('parameterId' => '174', 'fieldName' => 'gimme')
); 

$fields = $array;

$fieldId = 177; //yes, set somewhere else as a var.

$fieldArray = array_filter($fields, create_function('$fields', 'return $fields["parameterId"]==' . $fieldId . ';'));

$field = current($fieldArray); //since it's always the only one returned

$urlField =  $field['fieldName'];

Thanks again

Weedpacket

bagus wrote:
I assume that is actually somehow doing a foreach and only returning when it is true. Is that right?

Basically. What create_function returns is (the name of) a function which in your case is effectively

function \x00lambda_42($fields)
{
    return $fields["parameterId"]==177;
}

(The "\x00" in the function name is actually a NUL character and is surprisingly hard to type - this alone makes created functions less than useful in more extensive contexts; despite how much I like functional programming I hardly ever use create_function.) Then array_filter will go looping through the array you've given it (internally, without using additional PHP constructs) building a new array with all of the elements for which that function returns true. Yes; that function remains sitting around for the remainder of the script. It's not so much a leak as a consequence of the fact that the same is true of all functions in PHP (because in general there is no way of knowing that a given function will never be needed again).

Whether that would avoid the out of memory error is a bit difficult to say without knowing more about the code that was causing it in the first place (the leak may actually occur earlier, but the limit is only reached once you're already in the loop).