Concatinate integer arrays iteratively

Question

I have a methode in2.getImagesOneDim() which gives me an array of integers, to be more precise the pixel values of an image. Now i want to create one big array with all the pixel values of all the images. Therefore I have to call this method several times. Now I would like to concatenate the previous output to the current output until all images are read.

In some kind of pseudo code, where the + is a concatination ... :

 for (int i = 1; i < 25; i++) {
  ConArray = ConArray + in2.getImagesOneDim("../images/"+i);
 }

How would I do this in java ?

It is just pseudo code. I see it as the total array with all the pixel values — Olivier_s_j
– Olivier_s_j, Commented Nov 18, 2012 at 10:48
You already know the size is gonna be 24, why not just use an array? — Sietse
– Sietse, Commented Nov 18, 2012 at 10:49
because the in2.getImagesOneDim method does not return 1 value, it returns an array with a variable length of pixels. Therefore it is not possible to get the exact size of the eventual array — Olivier_s_j
– Olivier_s_j, Commented Nov 18, 2012 at 10:52

Michał Ziober · Accepted Answer · 2012-11-18 11:34:44Z

1

Split big problem into many smaller and You find the way:

Read each image into separate array
Compute total size
Join sub arrays

See example

import java.util.Arrays;

public class ImageProgram {

    public static void main(String[] args) {
        System.out.println(Arrays.toString(new ImageReader().readImages()));
    }
}

class ImageReader {

    public int[] readImages() {
        int[][] images = readImagesInto2DArray();
        return makeOneDimensionArray(images);
    }

    private int[] makeOneDimensionArray(int[][] arrays) {
        int totalLength = computeTotalLength(arrays);
        int[] array = new int[totalLength];
        int destPos = 0;
        for (int[] subArray : arrays) {
            System.arraycopy(subArray, 0, array, destPos, subArray.length);
            destPos += subArray.length;
        }
        return array;
    }

    private int computeTotalLength(int[][] arrays) {
        int length = 0;
        for (int[] subArray : arrays) {
            length += subArray.length;
        }
        return length;
    }

    private int[][] readImagesInto2DArray() {
        int size = 24;
        int[][] result = new int[size][];
        for (int i = 0; i < size; i++) {
            result[i] = readArray(i + 1);
        }
        return result;
    }

    private int[] readArray(int index) {
        // read from file
        int[] result = new int[index];
        Arrays.fill(result, index);
        return result;
    }
}

answered Nov 18, 2012 at 11:34

Michał Ziober

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2 Comments

Olivier_s_j Over a year ago

where would my method come into place ? (in2.getImagesOneDim("../images/"+i)), which returns an array of int

Michał Ziober Over a year ago

Use Your method instead of my "readArray" method. You could put "in2" object as a argument to method "readImages".

Sietse · Accepted Answer · 2012-11-18 10:56:59Z

0

List<int[]> pixels = new ArrayList<int[]>();
for (int i = 1; i < 25; i++) {
    pixels.add(in2.getImagesOneDim("../images/"+i));
}
return pixels;

Now you have a list of all the data, you can get the data with pixels.get(index);

edited Nov 18, 2012 at 10:56

answered Nov 18, 2012 at 10:51

Sietse

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5 Comments

Olivier_s_j Over a year ago

I need an array, not an arraylist, this gives me an array list of arrays ..., how would the conversion to an array work?

Sietse Over a year ago

@Ojtwist Sorry, I don't think you can convert it in an array. But you can just use pixels.get(5) instead of pixels[5]. Works the same.

Olivier_s_j Over a year ago

That is not an option in my framework, it is supposed to work on the GPU with JOCL and it does not allow arraylists

Sietse Over a year ago

@Ojtwist I am not familiar with JOCL, but can't you send them one by one?

Olivier_s_j Over a year ago

That would defy the purpose of running it on a GPU or generally parallel. I need one big array of values :)

The Cat · Accepted Answer · 2012-11-18 11:20:39Z

0

You could use the Collections#addAll method.

List<Integer> allIntegers = new ArrayList<Integer>();

for (int i = 1; i < 25; i++) {
    Integer[] imageIntegers = in2.getImagesOneDim("../images/"+i);
    allIntegers.addAll(Arrays.asList(imageIntegers));
}

return allIntegers.toArray();

answered Nov 18, 2012 at 11:20

The Cat

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3 Comments

Olivier_s_j Over a year ago

Is it possible to work with int instead of Integer ? Because my framework does not allow for Integer just int.

The Cat Over a year ago

Well you can convert them if you have access to the apache lang package, commons.apache.org/lang/api-release/org/apache/commons/lang3/…

Michał Ziober Over a year ago

When You convert array to list, and then when You concatenate lists, and after all, when You convert list to array - JVM invokes a lot of "copy" and "resize" methods. To avoid this You should directly work on raw array

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