wood burning stoves 2.0*
The moose likes Java in General and the fly likes architectural advice on iterating over large datasets Big Moose Saloon
  Search | Java FAQ | Recent Topics | Flagged Topics | Hot Topics | Zero Replies
Register / Login
JavaRanch » Java Forums » Java » Java in General
Bookmark "architectural advice on iterating over large datasets" Watch "architectural advice on iterating over large datasets" New topic
Author

architectural advice on iterating over large datasets

Emilio Gagliardi
Greenhorn

Joined: Jun 02, 2004
Posts: 16
I am working on a project where one of the goals is to allow us to compare arrays of doubles. The data is currently stored in a file as 50000*50000 doubles; think of it as 50000 vectors with 50000 elements in each.
I need to process each vector to every other vector but I don't need to process a vector against itself or repeats. Futhermore, I can't store all the vectors in memory. What I need to do is this:
OUTER LOOP
read vector[i]//all from same file
INNER LOOP
read vector[j] //all from same file
compare and store value
i + j would look like this:[0,1][0,2][0,3][0,4][1,2][1,3][1,4][2,3][2,4]...etc, progressively iterating over the file until no more unique comparisons are possible.

Now the part I don't really understand is how I can keep track of which pairs I have compared so I'm not comparing [0,0][1,0][1,1][2,0][2,1][2,2] because either they already exist (0,1 is the same as 1,0) or I don't want to make the comparison (1,1). At first i thought I would simply load all the vectors into memory, but then realized I can't. But that leaves the problem of keeping track of which ones I have compared. Part of the problem is that I need to keep track of the values I produce when I compare the vectors so that I can sort them later.

That leads me to a whole new problem of how to store the vector comparisons, but that is further down the road.

SO I called this architectural advice because at this point I'm not sure how to think about processing the data and which data structures I should investigate utilizing. One glimor of an idea is that I could use a MappedByteBuffer but I'm not really sure how to implement that to solve my problem.

Any advice or suggestions are greatly appreciated.
[ June 10, 2004: Message edited by: Emilio Gagliardi ]

Emilio
Tim West
Ranch Hand

Joined: Mar 15, 2004
Posts: 539
I'm not sure from your description exactly what you're computing, but one idea - you could determine whether or not two of the vectors are identical by computing their hashcodes and storing those in memory.

Could you be a bit more specific about what you do when you compare two arrays? I couldn't work out what was supposed to be unique...but it is early in the morning here, maybe I'll wake up soon =)


--Tim
Emilio Gagliardi
Greenhorn

Joined: Jun 02, 2004
Posts: 16
HI Tim;
I think after this project I'll owe you a beer or three

I need to calculate the Euclidian distance between each vector. The unique part comes from the fact that the distance between vector m and n is the same as the distance between vector n and m. Meaning, once I've computed the distance between any two vectors (a compared to b), I don't need to calculate the distance from the perspective of the other vector (b compared to a) nor do I need to calculate the distance between a and a!

How exactly do you compute the hashcode of an array?? That sounds promising! I'm curious about how to compute hashcodes but I don't really get what is hashed.

Cheers,
 
wood burning stoves
 
subject: architectural advice on iterating over large datasets
 
Similar Threads
JTable; Vectors & Boolean values
commit() and rollback() problem!
compare data in 2 vectors
setting focus
want to display results page by page