Joining up to 3 values in an array in a loop

I am trying to run some logical tests and matching a list of strings against a database but need help with the array I have.

the Problem

I have an array:

$myArray =
array([0] (
   array [0] ([0] A, [1] B, [2] C, [3] H)
   array [1] ([0] A, [1] D, [2] G, [3] H, [4] L)
   array [2] ([0] D, [1] Z, [2] J, [3] K, [4] O, [5] X)
)
array([1] (
   array [2] ([0] F, [1] Y, [2] W, [3] H, [4] L)
)
array([2] (
   array [0] ([0] O, [1] T, [2] C, [4] O, [5] X)
   array [1] ([0] U, [1] E, [2] E, [3] D)
))

I am trying to test the strings in this array against a list that combines 1, 2 and 3 strings combined with '_' in a table.
Example: A or A_B or A_B_C

Variables and Constants

The array length can vary in each of the second dimension of the array
Strings can be repeated several times and it has no bearing on the logic
The constant however is that the test to combine two strings or three strings is always sequential (e.g. always A_B or A_B_C and not A_D or A_D_J if that makes sense)
The sequence moves by one letter each time e.g. first test (A_B_C, A_B and A), then test (B_C_D, B_C and B), then (C_D_E etc...)
When the array has insufficient strings to continue testing 2 or 3 combined words, then the test should just run on 1 string

What I am trying to do and desired outcome

I need help with the array syntax to help me build the code into a 3 level logical argument in a loop

something like this:
IF A_B_C exists in myTable do something
ELSE IF A_B exists do something else
ELSE IF A exists do yet another thing
ELSE return blank

I can't quite figure out however how to manipulate the above array so as to arrive at variables

$firstTest = 'A_B_C'; <br>
$secondTest = 'A_B'; <br>
$thirdTest = 'A'; <br>

(I can get thirdTest)

What I tried

through receiving some useful help on other array questions, I tried passing the $myArray through a foreach loop as follow:

foreach ($myArray as $newArray) {
$i = 0;
$j = $i++;

foreach($newArray as $key=>$val) {
    $impArray = array($val[$i],$val[$j]);
    echo implode('_', $impArray);
}
}

However this takes the first string of each first level array.

EDIT:

I have been experimenting with array_slice and do while and can almost get there but the pattern does not quite follow a 3x string combination; instead, it increases from 3 strings to 4 strings, to 5 strings etc... and I do not know why.

Here is my latest attempts:

foreach ($myArray as $newArray => $val) {
    $x = 0;
    $z = 3;
    $route = array();
    
    do  {

        $route = array_slice($val, $x , $z);
        $imp_route = implode('_', $route);
        echo $imp_route;
        $x++;
        $z++;
    } while ( $z <= count($val));
}

Solution

Maybe there's a fancier way to do it, but this way makes it clear what you're trying to accomplish:

foreach ($myArray as $newArray) {
    foreach ($newArray as $valuesArray) {
        for ($i=0; $i<count($valuesArray); $i++) {
            // A_B_C
            if (isset($valuesArray[$i+2])) {
                echo $valuesArray[$i] . '_' . $valuesArray[$i+1] . '_' . $valuesArray[$i+2];
            }
            // A_B
            if (isset($valuesArray[$i+1])) {
                echo $valuesArray[$i] . '_' . $valuesArray[$i+1];
            }
            // A
            echo $valuesArray[$i];
        }
    }
}