When you search in Google "100F to C" how does it know to convert from Fahrenheit to Celsius? Similarly, conversion from different currencies and simple calculation.
What is the data structure used, or is it simple pattern matching the strings?
A:
it's simple pattern matching
try
100 kmh in mph = no calculation
100 kph in mph = 62.1371192 mph
Martin Beckett
2010-03-28 17:38:43
"100 km/h in mph" works though: km/h is the correct abbreviation
gbn
2010-03-28 17:40:26
I'm almost 100% sure that for mathematical expressions (e.g. 100 * (6 +3)) they use a parser as they are non-regular.
DrJokepu
2010-03-28 17:41:29
@DrJokepu: agreed, but there is the harder problem of recognizing it is a suitable expression for sending to the calculator prior to treating it as a search string. I'm guessing there's a pile of regexps and heuristics for that determination.
msw
2010-03-28 18:08:53
@gbn thats my point it just looks for a bunch of strings. Of course if km/h is correct then it should also require mi/h. You can't have too many alternatives in your lookup or you will try and eval everything as a calculation.
Martin Beckett
2010-03-28 18:15:52
+1
A:
It's not exactly simple pattern matching. Evaluating the mathematical expressions you can enter is not trivial. For example, here's an algorithm that evaluates a math expression. That's just the evaluation, there's probably a lot of code to detect if it's even valid.
For the currencies conversion and other units, that's simple pattern matching.
IVlad
2010-03-28 18:56:15