如何将原始双精度数组转换为双精度数组

Question

With the Apache common math library I get back a primitive double array.

  RealMatrix pInverse = new LUDecomposition(p).getSolver().getInverse();

  double[][] temp = pInverse.getData();

I need to convert temp to a Double[][]

  Double[][] inverse = new Double[][]temp;

Answer 1

If you are using Java 8+ you can use :

Double[][] inverse = Arrays.stream(temp)
        .map(d -> Arrays.stream(d).boxed().toArray(Double[]::new))
        .toArray(Double[][]::new);

Answer 2

As you are already using Apache Commons , it might be worth pointing out ArrayUtils.toObject

Converts an array of primitive doubles to objects.

Using that, you could write Andreas first solution as

Double[][] inverse = new Double[temp.length][];
for (int i = 0; i < temp.length; i++) {
    inverse[i] =  ArrayUtils.toObject(temp[i]);
}

or YCF_L's solution as

Double[][] inverse = Arrays.stream(temp)
    .map(ArrayUtils::toObject)
    .toArray(Double[][]::new);

Answer 3

It's a simple set of nested loop:

Double[][] inverse = new Double[temp.length][];
for (int i = 0; i < temp.length; i++) {
    inverse[i] = new Double[temp[i].length];
    for (int j = 0; j < temp[i].length; j++)
        inverse[i][j] = temp[i][j];
}

It's even shorter if you know all the sub-arrays are the same size:

Double[][] inverse = new Double[temp.length][temp[0].length];
for (int i = 0; i < temp.length; i++)
    for (int j = 0; j < temp[0].length; j++)
        inverse[i][j] = temp[i][j];