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Save matrix to a file in way to use it in a future

I need to store a large matrix for future extracting some values from it. I am new in Java, so I don't know how exactly it can be done. Does somebody knows how it can be realized?

[187 byte] By [Neludoffa] at [2007-11-27 5:30:47]

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# 1

You can write the matrix to a text file. Each row of the matrix is a line in the file, with individual elements separated by spaces, commas, or whatever you want. When you load it, read each line, and parse the individual values out into ints.

hunter9000a at 2007-7-12 14:55:22 >

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# 2

Yes, that's the decision. But here I'm loading a huge matrix again in a memory. Is it any way to get the particular value directly from a file?

Neludoffa at 2007-7-12 14:55:22 >

# 3

Write the matrix as a csv file. A csv file is an excel spread sheet. If you open it with a text editor you wil see the columns are comma delimited making it easier to parse.

kdajania at 2007-7-12 14:55:22 >

# 4

> Yes, that's the decision. But here I'm loading a huge

> matrix again in a memory. Is it any way to get the

> particular value directly from a file?

Generally it is relatively slow and inefficient to pick particular values from a file. HDs are good at getting to a sector and blasting lots of data

Anyway, another suggestion about storing matrix data, which I actually used is to serialize it to a file. If you've got a double[] or a double[][] it's a snap to serialize and deserialize this type of information

tjacobs01a at 2007-7-12 14:55:22 >

# 5

loads o' data == database

Hippolytea at 2007-7-12 14:55:22 >

# 6

Thanks everybody! I'll try with csv-file. Let's see how it will be work.

Neludoffa at 2007-7-12 14:55:22 >

# 7

Although a database is probably the best idea, there are things you can do when you store the data in a file to make it relatively quick to access individual pieces of data.

Store the data in fixed length format so that you can calculate the starting byte of any piece of information and read it using RandomAccessFile.

Example:

Matrix:

1 1 30 4

2 20 800 1

1 2 3 4

Store in file:

0001000100300004

0002002008000001

0001000200030004

Now to get the data in the 2nd row 4th element (1):

starting byte = ((row ?1) * 16) + ((column ?1) * 4)

((2 ?1) * 16) + ((4 - 1) * 4)

16 + 13 = 29

If you actually have newline characters in the file then you will need to adjust for them also but you should get the idea.

Also, if your data is numeric then you do not need to store the data as string representations of numbers; you can store the actual bytes that make up the int, long, etc.

And if you want to get really fancy you could create indexes to different elements...wait, I think they have a name for that already : )

Message was edited by:

jbish

jbisha at 2007-7-12 14:55:22 >

# 8

You cant just serialize the array to a file?

TuringPesta at 2007-7-12 14:55:22 >

# 9

> You cant just serialize the array to a file?Not if the OP wants to get a particular entry staight from the file (see reply #2) - well, you could but it would be cludgy.

jbisha at 2007-7-12 14:55:22 >

# 10

You haven't stated what you mean by a huge matrix. How big is huge? What does the matrix contain, can the elements be represented using the primitive types of Java? You say that you need to extract some values from it--are the values related in some way, are they close to each other?

Can the matrix fit on a hard drive without compression? If so and if you really have a lot of data, using a memory mapped file can be one solution.

If you have more than one big matrix that can fit in the computer's memory but you might have problems with fitting them all on the disk, you can treat them as images and compress them.

jsalonena at 2007-7-12 14:55:22 >

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Save matrix to a file in way to use it in a future

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