Running calculations on multi-dimensional arrays? - php

Question

This is probably a real simple question but I'm looking for the most memory efficient way of finding out data on a particular multi-dimensional array.
An example of the array:
[0] => Array(
[fin] => 2
[calc] => 23.34
[pos] => 6665
)
[1] => Array(
[fin] => 1
[calc] => 25.14
[pos] => 4543
)
[2] => Array(
[fin] => 7
[calc] => 21.45
[pos] => 4665
)
I need a method of identifying the values of the following things:
The max 'calc'
The min 'calc'
The max 'pos'
The min 'pos'
(you get the gist)
The only way I can think of is manually looping through each value and adjusting an integer so for example:
function find_lowest_calc($arr) {
$int = null;
foreach($arr['calc'] as $value) {
if($int == null || $int > $value) {
$int = $value;
}
}
return $int;
}
The obvious drawbacks of a method like this is I would have to create a new function for each value in the array (or at least implement a paramater to change the array key) and it will slow up the app by looping through the whole array 3 or more times just to get the values. The original array could have over a hundred values.
I would assume that there would be an internal function to gather all of (for example) the 'calc' values into a temporary single array so I could use the max function on it.
Any ideas?
Dan

Answer 1

$input = array(
array(
'fin' => 2
'calc' => 23.34
'pos' => 6665
),
array(
'fin' => 1
'calc' => 25.14
'pos' => 4543
),
array(
'fin' => 7
'calc' => 21.45
'pos' => 4665
)
);
$output = array(
'fin' => array(),
'calc' => array(),
'pos' => array(),
);
foreach ( $input as $data ) {
$output['fin'][] = $data['fin'];
$output['calc'][] = $data['calc'];
$output['pos'][] = $data['pos'];
}
max($output['fin']); // max fin
max($output['calc']); // max calc
min($output['fin']); // min fin

Answer 2

There is no way to speed that up, besides calculating all three values at once. The reason for this is that you always need to loop through the array to find the sub-arrays. Even if you find a bultin function, the time complexity will be the same. The only way to make a real difference is by using another datastructure (i.e, not any of the bultin ones, but one you write yourself).

Answer 3

How are you receiving the array? If it is your code which is creating the array, you could calculate the minimum and maximum values as you are reading in the data values:
$minCalc = null;
$arr = array();
for(...){
//read in 'calc' value
$subArr = array();
$subArr['calc'] = //...
if ($minCalc === null || $minCalc > $subArr['calc']){
$minCalc = $subArr['calc'];
}
//read in other values
//...
$arr[] = $subArr;
}
Also, in your find_lowest_calc function, you should use the triple equals operator (===) to determine whether the $int variable is null. This is because the statement $int == null will also return true if $int equals 0, because null equals 0 when converted to an integer.

Answer 4

You don't have to crate a new function for each value, just pass the key you want in the function
function find_lowest($arr, $indexkey) {
$int = null;
foreach($arr[$indexkey] as $value) {
if($int == null || $int > $value) {
$int = $value;
}
}
return $int;
}
As php is not type-safe, you should be fine passing both string or int index