Sorting 2D arrays

Programming Questions

roymond

in Programming Questions • 3 years ago

I haven't been able to find clear directions for sorting 2D arrays. I have to process data that is time based, but dependent on userIDs. What I am doing is putting userID, datetimestamp and a value in a 2D array. There are thousands of these rows:

userdata[i][1] = userID
userdata[i][2] = datetimestamp
userdata[i][3] = value

I need to sort on userID & datetimestamp in order to determine how to handle the associated values.

Any help appreciated.
roy

Replies(3)

kooogy

Re: Sorting 2D arrays

3 years ago

define a class for the three items. make it implement Comparable and write a comparator.

http://download.oracle.com/javase/tutorial/collections/interfaces/order.html (um, uses generics so processing 1.2.1 and above)

http://onjava.com/pub/a/onjava/2003/03/12/java_comp.html (older version)

kevin.bjo..

Re: Sorting 2D arrays

3 years ago

Are you sure that a 2D array is what you want for user data? I'd expect that such an array would be very sparsely populated. An ArrayList of ArrayLists (or something) might be more appropriate, faster, and more memory-sensible.

Depending on how you collect the data, the timestamps (or even IDs) might arrive already sorted...

kb, http://www.riftgame.com/

roymond

Re: Re: Sorting 2D arrays

3 years ago

Kevin - the data comes from server logs and every array row is fully populated. It is sorted by datetimestamp, but I need to group by datetimestamp within userIDs in order to determine user activity. Also, there may be entries for a particular userID across multiple logs. Thus it must be sorted by userID, them datetimestamp.

Kooogy - thanks. I will try to implement a comparator and let you know how it works out.

I realize there are better tools for reporting off pure data analysis, but I want to do it in Processing as it will eventually lead to visualizing this data as well.

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