Efficient use of arrays

[Matt_T_hat]

Now the fastest way to do this would be with an SQL SELECT statment but as this is not possible I need to have reasonable speed even with big arrays

Belo are my functions which are logically simple. However is there a way of getting the same results but less processor cycles?

    // returns array
    function all_x_where_y_equals($x, $y, $val, $from){
        $new = array();
        foreach ($from as $fr){
            if ($fr[$y] == $val){
                $new[] = $fr[$x]
            }
        }
        return $new;
    }
    
    // returns array
    function all_keys_where_y_equals($y, $val, $from){
        $new = array();
        foreach ($from as $k => $fr){
            if ($fr[$y] == $val){
                $new[] = $k
            }
        }
        return $new;
    } 

[penagate]

There are a huge number of built-in array functions:
http://au2.php.net/manual/en/ref.array.php

I daresay you could find two to do what you've done there, and most likely faster as well.

[Matt_T_hat]

There are a huge number of built-in array functions:
http://au2.php.net/manual/en/ref.array.php

I daresay you could find two to do what you've done there, and most likely faster as well.

I figure that an inherently itterative function (or evena call abck one would probably work. I know that there is a filter with call abck (no idea how to use it) but I wouldn't know what function to plumb for if it came and hit me with a large textbook.

Sandly while I have very much grasped the logic the fine practice of code itself sometimes gets the better of me.

[Matt_T_hat]

The other issue is are array_walk and array_filter and faster than itteratin (which we do anyway)?

There seems to be a lack of flexability (that or I'm not getting the full scope of passing an array as a callback argument...

http://au2.php.net/manual/en/languag...types.callback

EDIT: I think my problem is tat I want to define paramiters in my itteration at call time containing some values supplied at runtime. I know that basic set opperatons exist for arrays. I don't know much about them would they be of use though?

[penagate]

You don't pass the array to the callback parameter. The callback is a reference to a function that you write to implement your comparison logic. In this case the $x/$y business in your code (which I have not quite figured out - me a bit slow this morning).

For example:

$numbers = array(1, 2, 3, 4, 5, 6, 7, 8);

function odd($x)
{
  return $x & 1;
}

$odd_numbers = array_filter($numbers, "odd"); 

Bah... I just noticed they used this example on the doc page as well. But that's the gist of it.

[Matt_T_hat]

You don't pass the array to the callback parameter. The callback is a reference to a function that you write to implement your comparison logic. In this case the $x/$y business in your code (which I have not quite figured out - me a bit slow this morning).

For example:

$numbers = array(1, 2, 3, 4, 5, 6, 7, 8);

function odd($x)
{
  return $x & 1;
}

$odd_numbers = array_filter($numbers, "odd"); 

Bah... I just noticed they used this example on the doc page as well. But that's the gist of it.

I followed that well enough, perhaps if I cover what I'm up to in the function I will crack it or enlighten you as to how odd I am (watever happens soonest).

Example data

Array(
  0 => array('foo' => 1, 'bar' => 45),
  1 => array('foo' => 77, 'bar' => 'yomama'),
  2 => array('foo' => 'cats', 'bar' => 'ags')
)

Thing is the real array migh be huge it is identical to piles of rows from a atabase (because in any other system it would be)

I want to be able to do the code only equivilant of "SELECT * FROM TABLE WHERE FIELD=VALUE"

so the first funcion returns all foo where bar=var and the second gets the keys (row numbers for all rows where bar=var).

The quickest is just to inspect them all

Now with array_filter (my best bet I think) I can go

$bob = array_filter($mybigfatarray, somefunctionIwrotethismorning); 

but how do I tell the function what the bar=var is that we are filtering for?

That's where I came unstuck. (it been a long day for me).

The other question is: is running a callback to itterate an array faster than itterating the array? If not what is. My worry is that the array could geta bit sizable (it's got to grow somewhat with use being part of a script designed to turn news into silliness via mapping words in a complex but interesting way untill the results are "funny").

[penagate]

function filter($x)
{
  return $x['bar'] == 'yomama';
}

$yomamas = array_filter($mybigfatarray, "filter"); 

?

[Matt_T_hat]

function filter($x)
{
  return $x['bar'] == 'yomama';
}

$yomamas = array_filter($mybigfatarray, "filter"); 

?

The problem is...

$yomamas = array_filter($mybigfatarray, "filter");
$yodadas = array_filter($mybigfatarray, "filter");
$yosista = array_filter($mybigfatarray, "filter"); 

[penagate]

$yomamas = array_filter($mybigfatarray, create_function('$x', 'return $x["bar"]=="yomama"'));
$yodadas = array_filter($mybigfatarray, create_function('$x', 'return $x["bar"]=="yodada"'));
$yosista = array_filter($mybigfatarray, create_function('$x', 'return $x["bar"]=="yosista"')); 

?

[Matt_T_hat]

Oooh that's good. I could make a nice wrapper for that.

[CornedBee]

Here's a version that doesn't require the ugly create_function. (PHP4 object syntax)

class elemequals_functor
{
  var $val;
  var $elem;
  function elemequals_functor($e, $v) { $this->elem = $e; $this->val = $v; }
  function run($a) { return $a[$e] == $val; }
}
function elemequals($e, $v)
{
  return array(new elemequals_functor($e, $v), 'run');
}

// For your particular case.
function bareq($v)
{
  return elemequals('bar', $v);
}

$yomamas = array_filter($mybigfatarray, bareq("yomama"));
$yodadas = array_filter($mybigfatarray, bareq("yodada"));
$yosistas = array_filter($mybigfatarray, bareq("yosista"));

[Matt_T_hat]

Here's a version that doesn't require the ugly create_function. (PHP4 object syntax)

Very clever. I think I follow all that.

Thank you.