转换2D ArrayList <Double> 到二维二维数组

Question

How I can convert a 2D ArrayList of double to a 2D array double ? I create a ArrayList<ArrayList<Double>> and I want to convert into a double [][]

I try this but the last line doesn't work and I don't know why?

double data[][] = new double [datalist.size()][];

    for (int i = 0; i < datalist.size(); i++) {
        ArrayList<Double> row = datalist.get(i);
        data[i] = row.toArray(new double[row.size()]);
    }

datalist is my 2D ArrayList , and I have an error with toArray() can you explain me why ?

Answer 1

Try the following:

Double data[][] = new Double [datalist.size()][];

for (int i = 0; i < datalist.size(); i++) {
    ArrayList<Double> row = datalist.get(i);
    data[i] = row.toArray(new Double[row.size()]);
}