Select a value from an array based on another array in php

Question

I have two arrays, percentiles and percentile_bounds and another int value total_score. Given the total score, I want to return the percentile in which this value is. Ie. I want to return a value from percentiles which corresponds to placing the total_score within the percentile_bounds. In python, I would do:

import numpy as np

percentiles = np.array([ 0,  5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95])
percentile_bounds = np.array([ 84, 104, 109, 115, 120, 123, 125, 127, 129, 132, 135, 136, 137, 139, 141, 145, 148, 151, 155, 159])

# example 1
total_score = 130
print(percentiles[np.where(percentile_bounds==(percentile_bounds[percentile_bounds<total_score][-1]))])
# 40

# example 2
total_score = 153
print(percentiles[np.where(percentile_bounds==(percentile_bounds[percentile_bounds<total_score][-1]))])
# 85

# example 3
total_score = 100
print(percentiles[np.where(percentile_bounds==(percentile_bounds[percentile_bounds<total_score][-1]))])
# 0

and I found a way in PHP (function sources: 1, 2) but it is very clumsy and long:

<?php
// Example 4
$total_score = 120;

$percentile_bounds = [84, 104, 109, 115, 120, 123, 125, 127, 129, 132, 135, 136, 137,139, 141, 145, 148, 151, 155, 159];
       
$percentiles = [0,  5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95];

// get the last element from percentile_bounds which is less than total_score
$value = end(array_filter($percentile_bounds, function ($x) use ($total_score) { return $x < $total_score; }));

// find its index
$key = array_search($value, $percentile_bounds);

// find the corresponding value in percentiles
echo "percentile: $percentiles[$key]";
// 15

Is there a better way of selecting the element from one array (percentiles) based on a position of an element (total_score) in the other array (percentile_bounds)?

Thanks

Note: it is not a duplicate of this.

Clarification: For total_score<=84 the result should be 0 (based on how percentiles work) but it also should not happen. In the code above I do not deal with this condition so it's ok not to but if the solution does, the better :). Thanks @jspit for pointing it out!

Why is this two arrays to begin with, why not one array that uses 0, 5, 10 etc. as keys? — C3roe
– C3roe, Commented Oct 28, 2021 at 11:20
I guess that's just because I think in python and not PHP :D. I have data, then from them, I get the percentiles and the bounds which are two different arrays, then I go back to PHP (I do not have the data within PHP). I didn't think of it as a dictionary. — My Work
– My Work, Commented Oct 28, 2021 at 11:22
@jspit, thanks, good point, in that case, it should be 0 (based on how percentiles work) but it also should not happen. — My Work
– My Work, Commented Oct 28, 2021 at 12:28

My Work · Accepted Answer · 2021-11-01 07:24:05Z

1

You can do it with this line where array_keys gives us an array of keys of our filtered array. end and max do the same job in this case because we have a sorted array and want to return its last index. So finally $percentiles[$lastIndexKeyOfOurFilteredArray] is what we print out:

echo $percentiles[max(array_keys(array_filter($percentile_bounds,function ($x) use ($total_score){return $x<$total_score; })))]

edited Nov 1, 2021 at 7:24

My Work

2,5605 gold badges28 silver badges57 bronze badges

answered Oct 28, 2021 at 12:51

keyhan

5222 silver badges7 bronze badges

Sign up to request clarification or add additional context in comments.

5 Comments

nima Over a year ago

While this code may answer the question, providing additional context regarding how and/or why it solves the problem would improve the answer's long-term value. You can find more information on how to write good answers in the help center: stackoverflow.com/help/how-to-answer . Good luck 🙂

My Work Over a year ago

what @nima writes is exactly what I would like to ask you. Could you please provide some explanations to your code? How it works, what it does etc., exactly as nima writes. Thanks

keyhan Over a year ago

Sure, array_keys gives us array of keys of our filtered array. end and max do the same job in this case because we have sorted array and want to return its last index. So finally $percentiles[$lastIndexKeyOfOurFilteredArray] is what we print out.

My Work Over a year ago

One more issue with this: if array_keys is empty (the value is less than any in thepercentile_bounds), the max function fails. How can it be fixed? The expected behaviour is to return 0.

keyhan Over a year ago

PHP max function will throw an E_WARNING error and return a boolean false because of empty array input. PHP internal type-casting conversion will convert the boolean false to integer 0 so you already have your expected 0. You can skip the warning with an "@" {echo @percentiles[max(arr...}. Obviously its just a trick for preserving single-line style of the code and its better to use if/else statement for validating data before passing to function to avoid errors.

User863 · Accepted Answer · 2021-11-01 07:38:47Z

1

foreach would be more readable and performant approach compared to array_filter

$total_score = 153;

$percentile_bounds = [84, 104, 109, 115, 120, 123, 125, 127, 129, 132, 135, 136, 137, 139, 141, 145, 148, 151, 155, 159];

$percentiles = [0, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95];

foreach ($percentile_bounds as $key => $bound) {
    if ($bound >= $total_score) {
        echo 'percentile: ' . $percentiles[max(0, $key - 1)];
        break;
    }
}

edited Nov 1, 2021 at 7:38

answered Oct 28, 2021 at 11:52

User863

20.1k3 gold badges20 silver badges45 bronze badges

4 Comments

jspit Over a year ago

echo "percentile: ".($key > 0 ? $percentiles[$key-1] : "??");

User863 Over a year ago

@jspit Good catch. thanks, buddy. we can use max() instead of ternary operator to resolve negative index

My Work Over a year ago

And I believe it's missing an equal sign: if ($bound >= $total_score) otherwise, the borders fall into the wrong interval. Also, would you have an explanation or reference for why it has better performance? Thanks

My Work Over a year ago

One more thing, it fails for $total_score>=160

Collectives™ on Stack Overflow

Select a value from an array based on another array in php

2 Answers 2

5 Comments

4 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

5 Comments

4 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related