A good use of str_split is reverse translating an amino acid sequence.
<?php
/* reverse translate an aa sequence using its dna counterpart */
function reverseTranslate($aaSeq,$ntSeq){
$nt=str_split($ntSeq,3);
$aa=str_split($aaSeq,1);
$gapChar=array('*','-');
$numAa=count($aa);
$ntIndex=0;
$newNtSeq="";
for($i=0;$i<$numAa;$i++){
// if the aa is a gap, then just put on a gap character
if(in_array($aa[$i],$gapChar)){
$newNtSeq.='---';
}
else{
$newNtSeq.=$nt[$ntIndex];
$ntIndex++;
}
}
return $newNtSeq;
}
?>