How to check if array values are almost same

Question

I have an array that contains seven numbers:

array(159.60, 159.60, 159.60, 159.60, 159.60, 199.50, 199.50);
array(395.68, 395.68, 395.68, 395.68, 395.68, 395.68, 395.68);
array(531.18, 531.18, 531.18, 531.19, 531.18, 531.18, 531.18);

I need to check if all values are same, with one twist: sometimes the values differ slightly because of rounding off errors (see 4th value in 3rd array). I want them considered same.

What would be the best way to check if all array values are same within a tolerance value, say 0.1.

Find the min/max elements and subtract them.

zerkms
– zerkms

2015-12-08 10:36:15 +00:00
Commented Dec 8, 2015 at 10:36 — zerkms
– zerkms, Commented Dec 8, 2015 at 10:36
@zerkms, you can actually write that as answer.

vish4071
– vish4071

2015-12-08 10:37:23 +00:00
Commented Dec 8, 2015 at 10:37 — vish4071
– vish4071, Commented Dec 8, 2015 at 10:37

Salman Arshad · Accepted Answer · 2015-12-08 11:14:01Z

2

For each array we can find the max & min value and check if it is greater than 0 or not as @zerkms suggested.

$tests = array(
    array(159.60, 159.60, 159.60, 159.60, 159.60, 199.50, 199.50), 
    array(395.68, 395.68, 395.68, 395.68, 395.68, 395.68, 395.68), 
    array(531.18, 531.18, 531.18, 531.19, 531.18, 531.18, 531.18)
);
foreach ($tests as $i => $test) {
    $result = abs(max($test) - min($test)) <= 0.1;
    var_dump($result);
}

Output

bool(false)
bool(true)
bool(true)

CODE

edited Dec 8, 2015 at 11:14

Salman Arshad

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answered Dec 8, 2015 at 10:41

Sougata Bose

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7 Comments

zerkms Over a year ago

That's funny you decided to remove credits to me :-D (not that it was important to me - but I find it curious that you initially put them then removed)

Sougata Bose Over a year ago

@zerkms I was updating the answers with some descriptions. You can see it now. Hope you get it.. :)

vish4071 Over a year ago

Not 0, but should be like: (max($ar) - min($ar)) <= tolerance

vish4071 Over a year ago

What are you doing...@Sougata? Not >0, but <=tolerance

zerkms Over a year ago

I'm off. I'm not even sure why something that takes 30 seconds to implement needs a 20 minutes discussion :-D

|

Liam Wiltshire · Accepted Answer · 2015-12-08 10:39:41Z

-1

You could write a pretty simple loop to check this:

function withinTolerance($array,$tolerance){
    $initialValue = $array[0]; //Set the initial value
    foreach ($array as $num){
        //Loop the array, and if the value is outside the tolerance, return false.
        if ($num < $initialValue - $tolerance || $num > $initialValue + $tolerance) return false;
    }

    return true;
}

answered Dec 8, 2015 at 10:39

Liam Wiltshire

1,26413 silver badges26 bronze badges

7 Comments

zerkms Over a year ago

This solution is broken: the 0-th element does not have any special properties so that you could rely on it.

vish4071 Over a year ago

bad answer. Say, tolerance=1, array= {5,6,4,5,5,5,5}. Your function returns true...it should, false.

zerkms Over a year ago

@SalmanA well, why not with element with index 1 or 42? What is the maths behind this magic: $num < $initialValue - $tolerance?

zerkms Over a year ago

@SalmanA are you sure you have come through all the comments to this answer?

zerkms Over a year ago

@SalmanA not sure what "incorrect" means. The second comment perfectly demonstrates the implementation flaw.

|

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