Initialize array of arrays

Question

I'm trying to make some test data with which to test some functionality of my code. To this end, I need a double[][]. I am trying to do with a function that takes a double[][] as an input parameter and copying onto it a local variable containing the test data. However, I get an error that I don't quite understand (I'm sure it's a very basic error, which is why I'm unable to Google it), understanding/fixing which I'd appreciate any help.

private void makeData(double[][] patterns)
{
    double[][] data = new double[2][];
    // exists so that I can change `data` easily, without having to change the core functionality of copying it over to `patterns`
    data[0] = {1.0,8.0}; // error!
    // copy over everything from data into patterns
}

The line marked in the above code is giving me the error Only assignment, call, increment, decrement, and new objects can be used as a statement. To this, my reaction is "Isn't data[0] = {1.0,8.0}; an assignment?

I'm fairly confused, so I'd appreciate any help

Answer 1

You want to do

data[0] = new[] {1.0, 8.0};

The curly brace initializers are only valid if you're creating an object/array. They don't work by themselves.

You can specify the type specifically:

data[0] = new double[] {1.0, 8.0};

But you don't have to if the compiler can infer the right type (which, in your case, it can).

Answer 2

Just replace:

data[0] = {1.0,8.0};

by:

data[0] = new double[] { 1.0, 8.0 };

The compiler has to know explicitly what to assign to data[0]. It doesn't infer it from the type of data[0].

Answer 3

You should to initialize your subarray first.

double[][] data = new double[2][];
data[0] = new double[] {1.0f, 8.0f};