在数组中找到最大值和父值

Question

I searched many thread but i can't find this solution I have this Array

Array 
( [0] => [1] => Array ( [0] => 2019-01-11T23:30:00CET [1] => -12.6 ) [2] => [3] => Array ( [0] => 2019-01-11T23:20:00CET [1] => -12.5 ) [4] => [5] => Array ( [0] => 2019-01-11T23:10:00CET [1] => -12.6 ) [10] => [11] => Array ( [0] => 2019-01-11T22:40:00CET [1] => -12.4 ) 

I found the path to have the maximum or minimum value ( Column [1] ) from this Array but i need to find the relative Parent

(example the minimum -12.6 is in the [1][0] as 2019-01-11T22:20:00CET) of this two values that are show in the first column ( Column[0] )

Thanks

Answer 1

If you use array_column() to extract the second column of your data, then you can use min() or max() with that array to pick which one you want. This code then extracts the ones that match using a foreach() and if to check if it matches (not exactly sure what you want as output, but this should help)...

$source = [["2019-01-11T23:30:00CET", -12.6],
    ["2019-01-11T23:20:00CET", -12.5],
    ["2019-01-11T23:10:00CET", -12.6]
];

$extract = min(array_column($source, 1));  // or use max()
$output = [];
foreach ($source as $key => $element) {
    if ( $element[1] == $extract )  {
        // Matches, so add to output
        $output[$key] = $element[0];
    }
}
print_r($output);

will give

Array
(
    [0] => 2019-01-11T23:30:00CET
    [2] => 2019-01-11T23:10:00CET
)

You could use array_filter() to extract the matching rows, but a foreach() is enough for a straightforward thing like this (IMHO).

If there is a possibility of blank values or strings in the value column, this may confuse the min() as it will consider the values and compare them as strings, to ensure they are all compared as numbers you can add...

$values = array_map("floatval", array_column($source, 1));
$extract = min($values);  // or use max()

The array_map("floatval",... goes through the list and converts them all to float values.

Answer 2

Also, here's a generalized algorithm-sketch for "finding the max in some array", expressed as pseudo-code:

• "Leave quietly" if the array is empty, or throw an exception.
• Otherwise, assume that the first element in the array is the biggest one.
• Now, loop through the remaining elements, testing if each one is, in fact, bigger than the "biggest one" that you have so far. If so, select it as the "biggest."
• When the loop is finished, return your answer.

Now – this is what a geek would call "an O(n) algorithm," which is to say that its execution-time will be "on the order of" the number of elements in the array. Well, if this is a "one-off" requirement, that's fine. Whereas if what you actually want to do is to get "more than one" max-element, sorting the array (once, then holding on to the sorted result ...) becomes significantly better, because the sort is going to be O(log(n)) ... "on the order of some logarithm of the number of elements," ... and the subsequent cost of "popping off" elements from that sorted array becomes non-existent.

There are other ways to do it, of course – trees and such - but I've already blathered-on too long here.