PHP preg_split adds a blank array key that can't be cleared by array_filter because there's a 'space' in it

import matplotlib.pyplot as plt
import numpy as np

plt.imshow(np.random.random((10,10)))
plt.plot([7], [7], 'ro')
plt.show()

$strings=['12jan','12 jan','12    jan','12/jan','12//jan','12/jan','12*/jan','12*//jan'];

foreach($strings as $string){
    var_export(preg_split('~(?<=[0-9])[*/ ]*(?=[a-z]+)~i',$string));
    echo "\n";
    var_export(preg_split('~\d+\K[*/ ]*~',$string));
    echo "\n";
    var_export(preg_match('~(\d+)[/* ]*([a-z]+)~i',$string,$out)?array_slice($out,1):'fail');
    echo "\n";
    var_export(preg_match('~(\d+)[/* ]*(.+)~',$string,$out)?array_slice($out,1):'fail');
    echo "\n";
    var_export(preg_match_all('~\d+|[a-z]+~i',$string,$out)?$out[0]:'fail');
    echo "\n---\n";
}

echo json_encode($filteredResult);

echo json_encode(array_values($filteredResult));