PHP Working with an array to find ranges and missing numbers - php

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.

Answer 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

Answer 2

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!