I developed a function for the same purpose in PHP because I wanted to see whether I can use it to analyse strings to figure out whether they're likely to be spam.
This is for the QWERTZ keyboard, but it can easily be changed. The first number in the array $keys is the approximate distance from the left and the second is the row number from top.
function string_distance($string){
if(mb_strlen($string)<2){
return NULL;
}
$keys=array(
'q'=>array(1,1),
'w'=>array(2,1),
'e'=>array(3,1),
'r'=>array(4,1),
't'=>array(5,1),
'z'=>array(6,1),
'u'=>array(7,1),
'i'=>array(8,1),
'o'=>array(9,1),
'p'=>array(10,1),
'a'=>array(1.25,2),
's'=>array(2.25,2),
'd'=>array(3.25,2),
'f'=>array(4.25,2),
'g'=>array(5.25,2),
'h'=>array(6.25,2),
'j'=>array(7.25,2),
'k'=>array(8.25,2),
'l'=>array(9.25,2),
'y'=>array(1.85,3),
'x'=>array(2.85,3),
'c'=>array(3.85,3),
'v'=>array(4.85,3),
'b'=>array(5.85,3),
'n'=>array(6.85,3),
'm'=>array(7.85,3)
);
$string=preg_replace("/[^a-z]+/",'',mb_strtolower($string));
for($i=0;$i+1<mb_strlen($string);$i++){
$char_a=mb_substr($string,$i,1);
$char_b=mb_substr($string,$i+1,1);
$a=abs($keys[$char_a][0]-$keys[$char_b][0]);
$b=abs($keys[$char_a][1]-$keys[$char_b][1]);
$distance=sqrt($a^2+$b^2);
$distances[]=$distance;
}
return array_sum($distances)/count($distances);
}
You can use it the following way.
string_distance('Boat'); # output 2.0332570942187
string_distance('HDxtaBQrGkjny'); # output 1.4580596252044
I used multibyte functions because I was thinking about extending it for other characters. One could extend it by checking the case of characters as well.
