is it possible to expand 2d array

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sha89red

is it possible to expand 2d array

in Programming Questions • 10 months ago

for example , I have
double[][] A = new double[3][3];

and i want to expand it like, let say

double[4][3]..

is it possible??
I tried expand(), but it only works for 1d array..any help,ideas are kindly appreciated..

Replies(5)

asimes

Re: is it possible to expand 2d array

10 months ago

This will expand one of the sub arrays. If you want to expand all the sub arrays then run the process through a for loop. Expanding the containing array does not seem to be as straightforward (although I never use expand()). It seems easier to just use an ArrayList of arrays for that. For expanding the sub arrays:

void setup() {
size(100, 100);
double[][] a = new double[3][3];
println("Before:");
for (int i = 0; i < 3; i++) println(a[i]);
println("After:");
a[0] = expand(a[0]);
for (int i = 0; i < 3; i++) println(a[i]);
exit();
}

A solution to needing to expand the containing "array":

ArrayList<double[]> b = new ArrayList<double[]>();

sha89red

Re: Re: is it possible to expand 2d array

10 months ago

Thanks for the reply..
I tried the first code but got this error : cannot convert from Object to double[]..at line 9

Does ArrayList<double[]> means each elements are double[] data type?? Which means that we already have 2d array??

Im thinking of using ArrayList, but trying to avoid that as I heard that it will use more memory and a bit slow(maybe Im wrong, just an amatuer,so not sure about that)..and also I had to re-write several arrays from double[][] to ArrayList and from an amateur experience I had, ArrayList is 1d array, so have to construct back to 2d array in loop and then have to convert the elements back to double as the elements in ArrayList are objects..Im not sure, but if Im wrong, please do tell me...

asimes

Re: is it possible to expand 2d array

10 months ago

The extra amount of memory that ArrayList uses is trivial. I am not 100% certain if Processing implements ArrayList like this, but I would image that an ArrayList is actually an array that starts at some size. Lets say that it starts with a length of 10. Every time you add an element it works like an array but once you add the 11th element it would be beyond what the array could hold so it doubles its size. Unless you plan on storing a crazy amount of information (like a million elements) you don't need to worry about that.

ArrayList<double[]> is storing elements that are arrays of type double. If you start with an empty ArrayList<double[]>:

ArrayList<double[]> a = new ArrayList<double[]>();

Then it just an empty ArrayList. The next thing to do would be to add a double[] element:

double[] firstOne = {
0.0, 1.0, 2.0
};
a.add(firstOne);

Now the ArrayList has one element in it which is a double array. You can keep adding as many double arrays as you want. To access the first double array do this:

a.get(0);

Here is the whole thing:

void setup() {
size(100, 100);
ArrayList<double[]> a = new ArrayList<double[]>();
double[] firstOne = {
0.0, 1.0, 2.0
};
a.add(firstOne);
println(a.get(0));
exit();
}

asimes

Re: is it possible to expand 2d array

10 months ago

This might be helpful as well as the syntax for changing an element of one of the double arrays inside the ArrayList looks a little weird:

void setup() {
size(100, 100);
ArrayList<double[]> a = new ArrayList<double[]>();
double[] firstOne = {
0.0, 1.0, 2.0
};
a.add(firstOne);
println("Before:");
println(a.get(0));
println("After:");
a.get(0)[2] = 5.0;
println(a.get(0));
exit();
}

sha89red

Re: Re: is it possible to expand 2d array

10 months ago

Thanks asimes!!
I appreciate your help..
I learned something new to me..

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