How to sort an Array ArrayList?

Processing Beginners
1

Hi!
I am working on a sorting algorithm but I am still having some trouble. I have an array list
ArrayList<ArrayList<Float>> segs = new ArrayList<ArrayList<Float>>();
and I want to sort() (width the default function) the ArrayList of Floats - segs.get(0).sort() (something like this but it doesn’t work)

How do I do it?

2 


import java.util.Collections;  // Import the Collections class

ArrayList <Float> list = new ArrayList();

list. add (17.1); 
list. add (7.7);
list. add (12.9);

println(list); 

Collections.sort(list); 

println(list);
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3

Hey!

Tested and working:

import java.util.Collections; //import Collections

ArrayList<ArrayList<Float>> segs = new ArrayList<ArrayList<Float>>();//your array

//Fill your array with random float values
for(int i=0; i<100; i++){
  segs.add(new ArrayList<Float>());
  
  for(int j=0; j<100; j++)
    segs.get(i).add(random(0,10));
}

printArray(segs.get(0)); //display the first row of seg

Collections.sort(segs.get(0)); //sort it by using Collections

printArray(segs.get(0)); //display the first row of seg sorted

You can achieve what you want by using the Collections class (you just give it your ArrayList and he do the job)

4

Alternatively you can use the faster FloatList container and its method sort():

5 


import java.util.Collections;  // Import the Collections class

ArrayList <ArrayList <Float> > list = new ArrayList();

// --------------------------------------------------------------------------------

ArrayList <Float> listA = new ArrayList();

listA.add (17.1); 
listA.add (7.7);
listA.add (12.9);

list.add(listA); 

listA=null; 

// -----------------------------------------------
// Use 

println(list.get(0));  

Collections.sort(list.get(0)); 

println(list.get(0));
6

Oh yes! An ArrayList of FloatList might be nicer!

How is FloatList faster than ArrayList? (and how much?)

7

FloatList is backed by an internal float[] array while the corresponding ArrayList<Float> is a Float array instead:
https://docs.Oracle.com/en/java/javase/11/docs/api/java.base/java/lang/Float.html

The primitive float type is faster than an object Float, but nothing that big.

Here’s an example using that combo:

import java.util.List;

final List<FloatList> segs = new ArrayList<FloatList>();

for (int i = 0; i++ < 3; ) {
  final FloatList fl = new FloatList();
  segs.add(fl);
  for (int j = 0; j++ < 5; fl.append(random(-1000, 1000)));
}

for (final FloatList fl : segs)  println(fl);
println();

for (final FloatList fl : segs)  fl.sort();
for (final FloatList fl : segs)  println(fl);

exit();

And that same sketch but using a vanilla FloatList[] array instead:

final FloatList[] segs = new FloatList[3];

for (int i = 0; i < segs.length; ++i) {
  final FloatList fl = new FloatList();
  segs[i] = fl;
  for (int j = 0; j++ < 5; fl.append(random(-1000, 1000)));
}

for (final FloatList fl : segs)  println(fl);
println();

for (final FloatList fl : segs)  fl.sort();
for (final FloatList fl : segs)  println(fl);

exit();
8

ArrayList<ArrayList<Float>> segs = new ArrayList<ArrayList<Float>>();

In my opinion this is hard to read and to maintain.

Instead make a class MyFLoatClass and an Arraylist of that

Arraylist<MyFLoatClass> list = new ArrayList();

Inside the class MyFLoatClass have another ArrayList.

Much clearer.

Chrisir

9

to be honest I was trying to make the sort() as a placeholder until I code my own, but it looks like it is even more difficult : P

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