Reverse order of the Arrays stored in ArrayList

Question

I'm working with Processing and IGeo library and I have an ArrayList of IVec[] arrays:

ArrayList<IVec []> v = new ArrayList<IVec[]>();

For every I of the ArrayList I have a collection of IVec [] arrays that represent the coordinates of the control points of a curve. I need to reverse the order of the IVec [] control points keeping the same order of the ArrayList (I'm trying to invert curve seam reversing control points order and keeping the original order of the curves) but I can't understand how to do this. Can anyone help me?

Maroun · Accepted Answer · 2015-09-02 08:03:40Z

1

I won't provide you a full solution, but will guide you through it:

Iterate on the array list v
for each item in it (IVec[]),
- Convert the array to a collection (for example using Arrays.asList)
- Use Collections.reverse to reverse the items in the list
- Conver it back to an array

answered Sep 2, 2015 at 8:03

Maroun

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3 Comments

liuz_m Over a year ago

When I try to use Arrays.AsList I get the error The function AsList(IVec[]) does not exist, I supposed related to IVec[] properties but not sure. I'm trying to iterate over the ArrayList to change the index manually with the for loop.

Maroun Over a year ago

@liuz_m it's asList, with small a.

liuz_m Over a year ago

Thank you for your help! I have corrected my mistake but now I get cannot convert from List<IVec>to List

code_dredd · Accepted Answer · 2015-09-02 08:28:40Z

1

You can use Collections.reverse

You can also use a stack data structure. You can iterate over collection you wish to reverse by pushing the elements into the stack. Then, when you actually want to use the elements, you pop each element from the stack, which will allow you to iterate over the collection in reverse order.

edited Sep 2, 2015 at 8:28

answered Sep 2, 2015 at 8:04

code_dredd

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Comments

liuz_m · Accepted Answer · 2015-09-02 10:39:38Z

0

This solution is working:

for (int i=0; i<v.size (); i++) {  
  IVec [] vert=v.get(i); 
  for (int j=0; j<vert.length/2; j++) {
    IVec temp = vert[j];
    vert[j]=vert[vert.length -1 - j];
    vert[vert.length - 1 - j] = temp;
  }
}

answered Sep 2, 2015 at 10:39

liuz_m

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Comments

Want2bExpert · Accepted Answer · 2015-09-02 11:03:27Z

0

Try this;

Create a Helper method/function that takes and returns array.
Inside the Helper method, use Collections.reverse
return the reversed array.
call this helper method inside a loop as below:

for(int i = 0; i < OutArray.length; I++)
{ // Here get the inner Array and pass it to Helper method. 
// Add the return array to newArray List 
}
return newArrayList.

edited Sep 2, 2015 at 11:03

answered Sep 2, 2015 at 8:21

Want2bExpert

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1 Comment

code_dredd Over a year ago

This post should elaborate on the solution rather than just post code and expect users to perform blind copy-pastes with getting additional understanding.

Chaos Monkey · Accepted Answer · 2015-09-02 11:34:14Z

0

This should work (not the most efficient way, but easily understood):

public static <T> void reverseElements(ArrayList<T[]> list) {   

    ArrayList<T> tempList = new ArrayList<T>();
    for(T[] arr : list) {

        tempList.clear();
        for(T t : arr)
            tempList.add(t);

        Collections.reverse(tempList);
        tempList.toArray(arr);
        arr = tempList.toArray(arr);
    }       
}

answered Sep 2, 2015 at 11:34

Chaos Monkey

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