2D ArrayList

Programming Questions

brokenbeep

in Programming Questions • 2 years ago

Hi everyone, I have a question regarding setting up a 2D ArrayList. I am copying data from an FFT array into an ArrayList like this:

//-------------------------------------------------------//get our spectrum data

myFFT.getSpectrum(myChannel);

//-------------------------------------------------------//write values to our ArrayList

myArrayList.add(myFFT.spectrum[1]);

}

Everything is working up to a point, I am adding data from position [1] of myFFT.spectrum and storing it into an ArrayList so that I have a dynamic record of how position [1] changes over time; the problem now is that there are 256 array locations in myFFT.spectrum and I would like to store all of them into a 2D ArrayList so that I have a record of how they all change over time.

I'll be honest, being fairly new to Processing, I'm really not sure how to do this! Do I have to declare 256 separate ArrayLists?! If not, how would I create an ArrayList with 256 positions to populate?

Many thanks in advance...

Replies(9)

nardove

Re: 2D ArrayList

2 years ago

Sure, try something like this

ArrayList<DataType>[] myArrayList = new ArrayList<DataType>[2];
// create the 2nd dimension
for ( int i = 0; i < myArrayList.size(); i++ ) {
myArrayList[i] = new ArrayList<DataType>();
myArrayList[i].add( new DataType() );
}

Basically all you need to do is to create a new array list for each cell in the array, you cal also do something like this:

ArrayList<ArrayList<DataType>> myArrayList = new ArrayList<ArrayList<DataType>>();

Hope that helps

brokenbeep

Re: 2D ArrayList

2 years ago

Hi, firstly thanks for the reply. As I said, I'm a bit of a noob at processing so I'm finding this a little hard to get through! I've tried replicating your method but there are a few things I don't quite get and I keep getting error messages

ArrayList<float>[] myArrayList = new ArrayList<float>[2];

I've tried running this but I get the following error message : "unexpected token float"

ArrayList<Float>[] myArrayList = new ArrayList<Float>[2];

I've tried running this but I get this error message : "Cannot create a generic array of ArrayList<Float>"

My first question would be, what the difference between "Float" and "float"? My second would be why are neither working and both returning error messages?

Looking a little further down your code, it looks to me (and I might well be wrong) that the 2nd dimension of the ArrayList is being dictated by size of the ArrayList, is that right? Could you talk me through that section a little more as I am having trouble working out why your doing it this way!

I might need to offer a little more information regarding what I want the programs to do. I am using an FFT library that outputs 256 streams of sound frequency information. I would like to take the information from these individual streams and copy them into their own ArrayList within a 2D ArrayList i.e stream 1 from the FFT would copy into ArrayList[1], stream 2 would copy in ArrayList[2] and so on. Currently I have been having to resort to these ugly botched up bits of code:

Creating the ArrayLists:

ArrayList myArrayList1 = new ArrayList();
ArrayList myArrayList2 = new ArrayList();
ArrayList myArrayList3 = new ArrayList();

And so on, individually creating ArrayLists up to 256....

Adding the FFT data to each ArrayList:

myArrayList1.add(myFFT.spectrum[1]);
myArrayList2.add(myFFT.spectrum[2]);
myArrayList3.add(myFFT.spectrum[3]);

And so on up to 256....

Using the ArrayLists contents to draw stuff within a function:

fftDraw (myArrayList1, 0); //d1=arrayList# name d2=depth
fftDraw (myArrayList2, 0.5);
fftDraw (myArrayList3, 1);

With (myArrayList#) individually going on up to 256.

I know there must be a much better way of doing this, I suspect it lies in writing to a 2D ArrayList. Any further help would be much appreciated! :)

PhiLho

Re: 2D ArrayList

1 years ago

Sorry as I only had a peek at the thread, but if you know in advance the number of items, you better use a simple array instead of an array list.
And you can make an array of array lists or of simple arrays.

fiveagon

Re: 2D ArrayList

1 years ago

// Won't compile
ArrayList<DataType>[] myArrayList = new ArrayList<DataType>[2];

@nardove: You can't mix Arrays and Generics like that. I think that the Generic type can be an Array though, like <Object[]>

@brokenbeep: I swear I've seen this thread before ...

Anyway, I retract my answer from whatever thread that was and I have to ask, why do you need to get the values from the FFT object and then put them into an ArrayList? It seems like these FFT objects would be way more useful than Floats.

Can a simple List of FFT objects work for you?

List<FFT> fourierList = new ArrayList<FFT>();

Then everytime you need an FFT "snapshot", you simply create a new one and add it to the List.

void draw() { // Or whatever loop you need to get all the FFT data over time
FFT currentFFT = new FFT();
currentFFT.getSpectrum(myChannel);
fourierList.add(currentFFT);
}

Which library are you using? I was looking at the Minum API and it doesn't seem to match up with what you've written.

brokenbeep

Re: 2D ArrayList

1 years ago

Thank you all so much for the replies!

@fiveagon: I'm using the Krister Ess FFT library.

I'm not sure if anyone will look into this for me, I would be incredibly grateful if they did, I've zipped the libraries and two of the patches I've been working on here in the hope that someone will take pity on me! If you run the patches, hold down "w" to see the graphics being drawn, press "x" to do a DXF export.

I'm coming up against two problems:

1) In both examples, the aim is to create a complete 3d visual representation of the sound played, with the hope of exporting it as a 3d DXF file. In the example "no_ArrayList" I've tried using a "for" loop, but the values keep getting over ridden; it doesn't present a complete picture of the past audio, something I understand but can't think of a way round. I've set it to remember the past 10 FFT windows with "int z" in the for loop, because values much higher than this slow down and threaten to crash the program.

2) In "Tundra_functioned", everything works much better, the values are written and remembered, but the code is very, very ugly and lengthy. It feels like I'm on the right path with this, it just isn't being executed very well!

The visuals do not need to be written in real time, I'm quite happy to load the FFT data into something, an arrayList, a List etc. and then generate the image afterwards with a keypress.

I really appreciate the help so far, thanks for all your input!

brokenbeep

Re: 2D ArrayList

1 years ago

The second example does work, but is proving very lengthy to code, currently I'm having to resort to this system (mentioned earlier in this thread) :

Creating the ArrayLists:

ArrayList myArrayList1 = new ArrayList();
ArrayList myArrayList2 = new ArrayList();
ArrayList myArrayList3 = new ArrayList();

And so on, individually creating ArrayLists up to 256....

Adding the FFT data to each ArrayList:

myArrayList1.add(myFFT.spectrum[1]);
myArrayList2.add(myFFT.spectrum[2]);
myArrayList3.add(myFFT.spectrum[3]);

And so on up to 256....

Using the ArrayLists contents to draw stuff within a function:

fftDraw (myArrayList1, 0); //d1=arrayList# name d2=depth
fftDraw (myArrayList2, 0.5);
fftDraw (myArrayList3, 1);

With (myArrayList#) individually going on up to 256.

I would have thought I could do this with a 3 "for" loops but I'm running into problems. When I try to create ArrayLists with a for loop using this code:

for (int i = 0; i < 100; i = i+1) {
ArrayList myArrayList(i) = new ArrayList();
}

I get "Syntax error, maybe missing a semicolon?". Also am I right in thinking that ArrayLists need to be declared in void setup() and "for" loops need to run within void draw() which might make this method impossible? Are there alternatives?

When I try to add data to the ArrayLists with the following code:

for (int i = 0; i < 100; i++) {
myArrayList(i).add(myFFT.spectrum[i]);
}

I get "The function myArrayList(int) does not exist. I also get this error message when I try to draw stuff using a for loop to access information within the ArrayLists.

I really don't understand these error messages. Is it possible to create ArrayLists in this way? Is it possible to access information from them like this?

fiveagon

Re: Re: 2D ArrayList

1 years ago

I really don't understand these error messages. Is it possible to create ArrayLists in this way? Is it possible to access information from them like this?

Nope. Syntax error means that the computer has no idea what you're trying to do.

I don't understand why you're putting only one float into each arraylist. What's the point? Do you put more in later?

Did you try my suggestions from earlier? I'm fairly certain that it will capture all the information you need. Keeping the FFT objects is faster, easier to code, easier to use, and way more useful (because you get to keep all the functions from the FFT class).

brokenbeep

Re: 2D ArrayList

1 years ago

Thanks for the reply fiveagon. Could you elaborate on why this doesn't work:

for (int i = 0; i < 100; i++) {
myArrayList(i).add(myFFT.spectrum[i]);
}

The logic seems to make perfect sense to me, I want to add myFFT.spectrum[1-100] to myArrayList[1-100] without having to write this 100 times! Not sure why the computer doesn't know what I want it to do!

I don't understand why putting only one float into each arraylist

I'm not putting just the one float into each ArrayList; each myFFT.spectrum[_] is spitting out a whole stream of floats and I'm storing them into a corresponding ArrayList.

Did you try my suggestion from earlier?

I tried my best but I could not find anything in the Processing reference regarding "List", I looked for it in my "Getting Started with Processing" book but also drew a blank. To be truthful, even though your suggestion might be pretty simple to implement for someone with more experience than me, I needed to find a tutorial or example to help me understand the concepts you were introducing. I'm so new to this language, I'm really just trying to find my feet!

PhiLho

Re: 2D ArrayList

1 years ago

" I could not find anything in the Processing reference regarding "List""
Look at the Java Reference...
It is a good idea to look up for unknown stuff, but not finding it doesn't prevent from using it...

fiveagon used a common idiom (in the Java world) of declaring a variable with an interface type, ie. a more generic type, as it adds extra flexibility: you can often replace new ArrayList() with another collection of the List family if the need arises. But in our simple case, a ArrayList<FFT> fourierList = new ArrayList<FFT>(); can work equally well. The <FFT> just declares the type of data you put in the list. If you try to put something else, the compiler will complain, and this allows to do .get() without casting.

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