In Java, read matrix with named rows and named columns from CSV

Question

I have a CSV file which contains a matrix of correlation coefficients between a set of objects (in the example below it is four objects u101, u102, u103, u104). The files uses the object names as row names and column names like so:

        u101,   u102,   u103,   u104
u101,   1.0,    0.2,    0.1,    0.4
u102,   0.2,    1.0,    0.5,    0.8
u103,   0.1,    0.5,    1.0,    0.9
u104,   0.4,    0.8,    0.9,    1.0

What I now need to do is: read the CSV file into some matrix format in Java such that I can access the correlation coefficients by name. Basically, I need to implement a function:

double getValue(String arg0, String arg1) {
    […]
}

When invoked with

getValue("u101", "u104")

the function should then return 0.4.

How can I do that?

Read 2D array from file (you'll probably want to use next for row/col names and nextDouble for cells). Convert String to row/col index - Map<String, Integer>. If the naming for row/col i is always u(101+i), then you can simply substring and parseInt. — Bernhard Barker
– Bernhard Barker, Commented Apr 3, 2013 at 14:29

Pradeep Pati · Accepted Answer · 2013-04-03 14:32:01Z

1

You would need 2 maps and a 2 dimensional array (or arraylist).

1st map should contain the col name as the key and the col position as value i.e. ('u101', 0), ('u102', 1) etc
2nd map should contain the row name as the key and the row postion as value
The 2d array should have the data, i.e. the numbers themselves

So when you get a call to your method, you do like

return myArray[rowmap.get('rowname')][colmap.get('colname')];

answered Apr 3, 2013 at 14:32

Pradeep Pati

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Community · Accepted Answer · 2017-05-23 12:29:17Z

0

To read doubles from a file: Reading double values from a file

Then store the values you read in a HashMap of doubles. Construct the hashmap keys using both the row and column name. To access the element at u102, u103 do:

hashmap.put("u102-u103", 0.5);
x = hashmap.get("u102-u103");

edited May 23, 2017 at 12:29

CommunityBot

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answered Apr 3, 2013 at 14:30

David

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1 Comment

Bernhard Barker Over a year ago

It may help to say a HashMap of what exactly you're suggesting.

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