Parsing a string for dates in PHP

Question

Given an arbitrary string, for example ("I'm going to play croquet next Friday" or "Gadzooks, is it 17th June already?"), how would you go about extracting the dates from there?

If this is looking like a good candidate for the too-hard basket, perhaps you could suggest an alternative. I want to be able to parse Twitter messages for dates. The tweets I'd be looking at would be ones which users are directing at this service, so they could be coached into using an easier format, however I'd like it to be as transparent as possible. Is there a good middle ground you could think of?

Answer 1

If you have the horsepower, you could try the following algorithm. I'm showing an example, and leaving the tedious work up to you :)

//Attempt to perform strtotime() on each contiguous subset of words...  //1st iteration strtotime("Gadzooks, is it 17th June already") strtotime("is it 17th June already") strtotime("it 17th June already") strtotime("17th June already") strtotime("June already") strtotime("already")  //2nd iteration strtotime("Gadzooks, is it 17th June") strtotime("is it 17th June") strtotime("17th June") //date! strtotime("June") //date!  //3rd iteration strtotime("Gadzooks, is it 17th") strtotime("is it 17th") strtotime("it 17th") strtotime("17th") //date!  //4th iteration strtotime("Gadzooks, is it") //etc 

And we can assume that strtotime("17th June") is more accurate than strtotime("17th") simply because it contains more words... i.e. "next Friday" will always be more accurate than "Friday".

Answer 2

I would do it this way:

First check if the entire string is a valid date with strtotime(). If so, you're done.

If not, determine how many words are in your string (split on whitespace for example). Let this number be n.

Loop over every n-1 word combination and use strtotime() to see if the phrase is a valid date. If so you've found the longest valid date string within your original string.

If not, loop over every n-2 word combination and use strtotime() to see if the phrase is a valid date. If so you've found the longest valid date string within your original string.

...and so on until you've found a valid date string or searched every single/individual word. By finding the longest matches, you'll get the most informed dates (if that makes sense). Since you're dealing with tweets, your strings will never be huge.