PHP Working with an array to find ranges and missing numbers

Question

I have an array that looks like this:

    [0] => Array
    (
        [1] => 5
        [2] => 4
        [3] => 3
        [5] => 1
        [7] => 1
        [8] => 2
        [9] => 3
        [10] => 4
        [11] => 5
    )

[1] => Array
    (
        [1] => 6
        [2] => 5
        [4] => 3
        [5] => 2
        [6] => 1
        [8] => 3
        [9] => 4
        [10] => 5
        [11] => 6
    )

[2] => Array
    (
        [1] => 7
        [2] => 6
        [3] => 5
        [4] => 4
        [5] => 3
        [6] => 2
        [7] => 3
        [8] => 4
        [11] => 7
    )

I have an order of operations I'm trying to go through and I really don't know where to go from here. Any suggestions would be of great help.

First I give my class the number of items I want to return. For example here we'll use 4.
I want to loop through and find the item in the array that has the lowest value.
I want to look at the keys to the items around (it included) and be sure they're not missing a number if they are..reject it..

In this example the first one you would come to would be:

    [5] => 1

Now looking around it you see that the keys are missing some numbers. So no combination of 4 will get that to match any 4 in the proper order.

    [1] => 5
    [2] => 4
    [3] => 3
    [5] => 1  //this one
    [7] => 1
    [8] => 2
    [9] => 3

In this situation I want it to move onto the next case.

    [7] => 1

Notice this one will work due to the keys being 7,8,9,10.

    [7] => 1
    [8] => 2
    [9] => 3
    [10] => 4

This is what I would like returned first..but I don't even know how to begin to get there.

Further more there are situations like this..Say for example there are no 1's at all in the dataset..and only this lone 2 in the last one.

    [0] => Array
    (
        [1] => 5
        [2] => 4
        [3] => 3
        [5] => 3
        [7] => 3
        [8] => 3
        [9] => 3
        [10] => 4
        [11] => 5
    )

[1] => Array
    (
        [1] => 6
        [2] => 5
        [4] => 3
        [5] => 3
        [6] => 3
        [8] => 3
        [9] => 4
        [10] => 5
        [11] => 6
    )

[2] => Array
    (
        [1] => 7
        [2] => 6
        [5] => 3
        [6] => 2 // this one
        [7] => 3
        [8] => 4
        [11] => 7
    )

The following wont work:

    [6] => 2 // this one
    [7] => 3
    [8] => 4
    [11] => 7

but this one will:

        [5] => 3
        [6] => 2 // this one
        [7] => 3
        [8] => 4

I have no idea on how to approach this.. If someone could offer some advice it would be GREATLY appreciated. Thanks so much in advance.

Unclear what you mean by "missing a number" - in your example, [6] is missing too, but [7] is accepted. Presumably if it's about to accept, say, [7], then the following x must exist? — Luke Briggs
– Luke Briggs, Commented Nov 16, 2016 at 16:39
Yes! If it's going to accept 7. Then I would want 4,5,6 to exist.. or 5,6,8..or 8,9,10...given that my initial input is only looking for 4. — Joel Has Simple Questions
– Joel Has Simple Questions, Commented Nov 16, 2016 at 16:43

Luke Briggs · Accepted Answer · 2016-11-16 17:01:18Z

1

The following assumes your data is in an array called $data. I'll describe it in steps, then pull it all together as a function.

Step 1 find the min value:

$minValue=min($data);

Step 2 loop through the array looking for all values that are that value:

foreach($data as $index => $value){

    if($value == $minValue){
         // $index is a candidate!
    }
}

Step 3 Check if $valuesToReturn entries exist after index:

    $success=true;

    for($i=1;$i<=$valuesToReturn;$i++){

        if(!array_key_exists($index + $i,$data)){

            // Candidate failed.
            $success=false;
            break;

        }

    }

Step 4 If the candidate was successful, return it.

    if($success){
        return $index;
    }

Putting that all together, we get this:

function findSuitableIndex($data,$valuesToReturn){

    // Min:
    $minValue=min($data);

    foreach($data as $index => $value){

        if($value == $minValue){
            // $index is a candidate!

            // test if index is actually suitable:
            $success=true;

            for($i=1;$i<=$valuesToReturn;$i++){

               if(!array_key_exists($index + $i,$data)){

                    // Candidate failed.
                    $success=false;
                    break;

                }

            }

            if($success){
                return $index;
            }

        }

    }

    // If we fell down here, we failed to find any successful results.
    return -1;
}

Working sample:

Code on eval.in

edited Nov 16, 2016 at 17:01

answered Nov 16, 2016 at 16:54

Luke Briggs

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7 Comments

Joel Has Simple Questions Over a year ago

WOW! You are my hero!!!! Now I just need to make it return the working 4 results in an array. I suggest everyone thumbs up this right now because it's perfect. Thank you so much!

Luke Briggs Over a year ago

@JoelHasSimpleQuestions no problem! I just quickly re-read the question so one thing that might catch you out: if $valuesToReturn is 4, then it'll check the 4 entries after the 'candidate' index. Change $i<=$valuesToReturn to $i<$valuesToReturn if you only want it to check the following 3 :) To return an array, the easiest thing to do is copy/paste that same for loop and do e.g. $result[]=$data[$index+$i];

Luke Briggs Over a year ago

@JoelHasSimpleQuestions My personal choice would be to do that last part in a separate function too - that way you can get just the index if it's useful.

Joel Has Simple Questions Over a year ago

Ok Awesome!!!!!! My hero. Big time. Any suggestions on finding 5,6,8? That's kind of the part where I'm really confused now.

Luke Briggs Over a year ago

@JoelHasSimpleQuestions how do you mean? I.e. what's it got to search for? :)

|

Sesh Sadasivam · Accepted Answer · 2016-11-16 16:46:21Z

Here are some suggestions. Your exact implementation would depend on your particular situation.

To loop through each element in the array, you could use a foreach loop.

foreach ($arr[0] as $index => $value) {
    // Here, $arr[0][$index] == $value;

}

To check if a key exists or not, you could use array_key_exists.

if ( !array_key_exists($index - 1, $arr[0]) ) {
    // The previous index is missing in the array.

}

A simple (but inefficient) way to find a contiguous sequence of k indices with the smallest value at the first index would be to find the smallest element and check if the contiguous sequence exists; if not, find the next smallest element and recursively check until you have completed processing the largest element.

You could also try finding all contiguous sequences of at least length k and then selecting the sequence with the smallest value at the first index.

Hope this helps!

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