Matrice.java

// indexed row matrix
        IndexedRowMatrix A = new IndexedRowMatrix(rddA.rdd());


        List<Double> stream = A.toRowMatrix().rows().toJavaRDD()
                // double[][] -> List<Double>
                .flatMap(v -> Arrays.stream(v.toArray()).boxed().iterator())
                .collect();

        // List<Double> -> double[]
        double[] arr = new double[stream.size()];
        for (int i = 0; i < stream.size(); i++) {
            arr[i] = stream.get(i);
        }

        DenseMatrix localMatrix = new DenseMatrix((int) A.numRows(), (int) A.numCols(), arr);