How do I create 2d arrays based on sparse column matrix parameters in Java?

Question

I am a new to Java. I want to create a 2d java arrays based on compressed sparse column matrix parameters. For example, I can create an 2d arrays by using the following code in python:

from scipy.sparse import csc_matrix

indices = [0, 2, 2, 0, 1, 2]
indptr = [0,2,3,6]
data = [1, 2, 3, 4, 5, 6]
shape = [3,3]
sp_mat = csc_matrix((data, indices, indptr), shape=shape).todense()
print(sp_mat)

[[1 0 4]
 [0 0 5]
 [2 3 6]]

But I don't know how to achieve it in Java.

import java.io.IOException;

public class Main {
    public static void main(String[] args) throws IOException {
        int[] indices = new int[]{0, 2, 2, 0, 1, 2};
        int[] indptr = new int[]{0, 2, 3, 6};
        int[] data = new int[]{1, 2, 3, 4, 5, 6};
        int[] shape = new int[]{3, 3};
        // some code to create 2D arrays
    }
}

I will have indices, indptr, data and shape 1d array as above code. I expect to be able to create the following 2d arrays:

int[][] sp_mat = new int[][]{{1, 0, 4}, {0, 0, 5}, {2, 3, 6}};

Answer 1

I finally found what I needed Java la4j library. First add dependencies:

<dependency>
    <groupId>org.la4j</groupId>
    <artifactId>la4j</artifactId>
    <version>0.6.0</version>
</dependency>

Then I can create CCSMatrix martix and convert matrix to 2d arrays.

import java.io.IOException;
import org.la4j.matrix.sparse.CCSMatrix;

public class Main {
    public static void main(String[] args) throws IOException {
        int[] indices = new int[]{0, 2, 2, 0, 1, 2};
        int[] indptr = new int[]{0, 2, 3, 6};
        double[] data = new int[]{1, 2, 3, 4, 5, 6};
        int[] shape = new int[]{3, 3};
        // some code to create 2D arrays
        CCSMatrix a = new CCSMatrix(
                shape[0], shape[1], data.length, data, indices, indptr);
        double[][] mat = a.toDenseMatrix().toArray();
    }
}