Fuzzy Matching on Date-Type values

Question

I don't have a real question but I'm more like seeking for creative input for a problem.

I want to compare two (most likely unequal) Date values and calculate the ratio of their similarity. So for example if I'd compare 08.01.2013 and 10.01.2013 I would get a relative high value but between 08.01.2013 and 17.04.1998it would be really low.

But now I'm not sure how I should exactly calculate the similarity. First I was thinking about turning the Date values into Strings and then use the EditDistance on them (number of single char operations to transform one String into another). This seems like a good idea for some cases and I'll definitly implement it but I also need an appropriate calculation for something like 31.01.2013 and 02.02.2013

Answer 1

Why not use the difference in days between two dates as a starting point? It is "low" for similar dates and "high" for unequal dates, then use arithmetic to obtain a "similarity ratio" which matches your requirements.

Consider a fixed reference date "early enough" in the past if you get stuck.

Answer 2

The edit distance can be calculated using the Levenshtein distance.

A change in the year would mean a lot more "distance" than a change in the day. The usual way to compare days would be to calculate the distance in days or hours. To do that, you'd convert both dates in a serial day number. Microsoft offers a DateDiff() function for date comparisons and distance calculations.