Array initialization question / problem.

Programming Questions

lukas.arv..

Array initialization question / problem.

in Programming Questions • 1 year ago

Hi!

I have a question regarding how array works. I will attch a small piece of sample code so you can see what I mean.

The first case is this, in a small processing application, I declare a float array named data. I pass that float array into the function loadData which returns a float array. The returned data is of correct length and with the correct values. So far so good.

float[] data;
public void setup()
{
data = chartData.loadData("oc", loadFileGdp);
}

But how does it work when I have a two dimensional array named data instead of a one dimensional? Like this example:

float[][] data;
String[] dataNames = new String[3];
dataNames[0] = "naData";
dataNames[1] = "euData";
dataNames[2] = "asData";
data = new float[dataNames.length][];
public void setup()
{
for(int i = 0; i < dataNames.length; i++)
{
data[i][] = chartData.loadData(dataNames[i], loadFileGdp);
}
}

I cannot get this to work, I know there are many workarounds that I can take to make it work, but I am interested to why this is wrong, to me it seems pretty logical.

Thank you very much for your help & many thanks to the processing team!

Kind regards,

Lukas

Replies(4)

quarks

Re: Array initialization question / problem.

1 year ago

For a start lines 4-8 cannot be executed outside of a method - move them to line 12.

In Java a 2D array aray is a 1D array of 1D arrays so you might need to change line 15 to

data[i] = chartData.loadData(dataNames[i], loadFileGdp);

since data[i] is a 1D array of floats and your first example indicates that loadData returns a 1D array of floats

HTH

lukas.arv..

Re: Array initialization question / problem.

1 year ago

Hi!

Thank you for the reply! Thanks for pointing out that I should move the lines. I created this little "representation" program here instead of copying the code I work on, so I didn't see that I had missed that.

You are correct that loadData is returing an 1D array of floats.

but it is correct to write like this: data = new float[dataNames.length][];

I want the returned float array from loadData to be passed into the "second" array of data, the one which has no specified length or size. Will the code below really accomplish this?

data[i] = chartData.loadData(dataNames[i], loadFileGdp);

Thanks for taking the time to help me!

//Lukas

quarks

Re: Array initialization question / problem.

1 year ago

but it is correct to write like this: data = new float[dataNames.length][];

Yes

I want the returned float array from loadData to be passed into the "second" array of data, the one which has no specified length or size. Will the code below really accomplish this?

data[i] = chartData.loadData(dataNames[i], loadFileGdp);

Yes - provided loadData returns a 1D array of floats

The following code is syntactically correct and proves what that this syntax works. You might notice the the arrays are not required to be the same length.

float[][] data;
String[] dataNames = new String[3];
public void setup(){
data = new float[dataNames.length][];
for (int i = 0; i < dataNames.length; i++) {
data[i] = new float[4 + i * 3];
print("Length of array " + i + " = ");
println(data[i].length);
}
print("Number of arrays = ");
println(data.length);
}

Produces the output

Length of array 0 = 4
Length of array 1 = 7
Length of array 2 = 10
Number of arrays = 3

lukas.arv..

Re: Re: Array initialization question / problem.

1 year ago

Thanks a lot for the excellent answer!!

//Lukas

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