Old question, but for anyone else coming across this I had to write up a solution to this today. The following takes a vaguely similar approach to the algorithm described by John Kugelman, but doesn't apply as strict a grammar; as such it will permit some weird orderings, e.g. "one hundred thousand and one million" will still produce the same as "one million and one hundred thousand" (1,100,000). Invalid bits (e.g. misspelled numbers) will be ignored, so the consider the output on invalid strings to be undefined.
Following user132513's comment on joebert's answer, I used Pear's Number_Words to generate test series. The following code scored 100% on numbers between 0 and 5,000,000 then 100% on a random sample of 100,000 numbers between 0 and 10,000,000 (it takes to long to run over the whole 10 billion series).
/**
* Convert a string such as "one hundred thousand" to 100000.00.
*
* @param string $data The numeric string.
*
* @return float or false on error
*/
function wordsToNumber($data) {
// Replace all number words with an equivalent numeric value
$data = strtr(
$data,
array(
'zero' => '0',
'a' => '1',
'one' => '1',
'two' => '2',
'three' => '3',
'four' => '4',
'five' => '5',
'six' => '6',
'seven' => '7',
'eight' => '8',
'nine' => '9',
'ten' => '10',
'eleven' => '11',
'twelve' => '12',
'thirteen' => '13',
'fourteen' => '14',
'fifteen' => '15',
'sixteen' => '16',
'seventeen' => '17',
'eighteen' => '18',
'nineteen' => '19',
'twenty' => '20',
'thirty' => '30',
'forty' => '40',
'fourty' => '40', // common misspelling
'fifty' => '50',
'sixty' => '60',
'seventy' => '70',
'eighty' => '80',
'ninety' => '90',
'hundred' => '100',
'thousand' => '1000',
'million' => '1000000',
'billion' => '1000000000',
'and' => '',
)
);
// Coerce all tokens to numbers
$parts = array_map(
function ($val) {
return floatval($val);
},
preg_split('/[\s-]+/', $data)
);
$stack = new SplStack; // Current work stack
$sum = 0; // Running total
$last = null;
foreach ($parts as $part) {
if (!$stack->isEmpty()) {
// We're part way through a phrase
if ($stack->top() > $part) {
// Decreasing step, e.g. from hundreds to ones
if ($last >= 1000) {
// If we drop from more than 1000 then we've finished the phrase
$sum += $stack->pop();
// This is the first element of a new phrase
$stack->push($part);
} else {
// Drop down from less than 1000, just addition
// e.g. "seventy one" -> "70 1" -> "70 + 1"
$stack->push($stack->pop() + $part);
}
} else {
// Increasing step, e.g ones to hundreds
$stack->push($stack->pop() * $part);
}
} else {
// This is the first element of a new phrase
$stack->push($part);
}
// Store the last processed part
$last = $part;
}
return $sum + $stack->pop();
}