RegEx or Similar - Grab string preceding matched value - php

Question

Here's the deal, I am handling a OCR text document and grabbing UPC information from it with RegEx. That part I've figured out. Then I query a database and if I don't have record of that UPC I need to go back to the text document and get the description of the product.
The format on the receipt is:
NAME OF ITEM 123456789012
OTHER NAME 987654321098
NAME 567890123456
So, when I go back the second time to find the name of the item I am at a complete loss. I know how to get to the line where the UPC is, but how can I use something like regex to get the name that precedes the UPC? Or some other method. I was thinking of somehow storing the entire line and then parsing it with PHP, but not sure how to get the line either.
Using PHP.

Answer 1

Get all of the names of the items indexed by their UPCs with a regex and preg_match_all():
$str = 'NAME OF ITEM 123456789012
OTHER NAME 987654321098
NAME 567890123456';
preg_match_all( '/^(.*?)\s+(\d+)/m', $str, $matches);
$items = array();
foreach( $matches[2] as $k => $upc) {
if( !isset( $items[$upc])) {
$items[$upc] = array( 'name' => $matches[1][$k], 'count' => 0);
}
$items[$upc]['count']++;
}
This forms $items so it looks like:
Array (
[123456789012] => NAME OF ITEM
[987654321098] => OTHER NAME
[567890123456] => NAME
)
Now, you can lookup any item name you want in O(1) time, as seen in this demo:
echo $items['987654321098']; // OTHER NAME

Answer 2

You can find the string preceding a value you know with the following regex:
$receipt = "NAME OF ITEM 123456789012\n" .
"OTHER NAME 987654321098\n" .
"NAME 567890123456";
$upc = '987654321098';
if (preg_match("/^(.*?) *{$upc}/m", $receipt, $matches)) {
$name = $matches[1];
var_dump($name);
}
The /m flag on the regex makes the ^ work properly with multi-line input.
The ? in (.*?) makes that part non-greedy, so it doesn't grab all the spaces

Answer 3

It would be simpler if you grabbed both the name and the number at the same time during the initial pass. Then, when you check the database to see if the number is present, you already have the name if you need to use it. Consider:
preg_match_all('^([A-Za-z ]+) (\d+)$', $document, $matches, PREG_SET_ORDER);
foreach ($matches as $match) {
$name = $match[1];
$number = $match[2];
if (!order_number_in_database($number)) {
save_new_order($number, $name);
}
}

Answer 4

You can use lookahead assertions to match string preceding the UPC.
http://php.net/manual/en/regexp.reference.assertions.php
By something like this: ^\S*(?=\s*123456789012) substituting the UPC with the UPC of the item you want to find.

Answer 5

I'm lazy, so I would just use one regex that gets both parts in one shot using matching groups. Then, I would call it every time and put each capture group into name and upc variables. For cases in which you need the name, just reference it.
Use this type of regex:
/([a-zA-Z ]+)\s*(\d*)/
Then you will have the name in the $1 matching group and the UPC the $2 matching group. Sorry, it's been a while since I've used php, so I can't give you an exact code snippet.
Note: the suggested regex assumes you'll only have letters or spaces in your "names" if that's not the case, you'll have to expand the character class.