Calling function from several vectors ordered by element value

Question

I have several vectors of different elements but all extending a class which has a specific function, lets say for example

Vector<classone> one;
Vector<classtwo> two;
Vector<classthree> three;

and classone, classtwo and classthree extend Number, and number has two functions:

doThing()
getValue()

And what i want is to call doThing in the order of the getValues received from all the vectors.

One cheap solution would be to concatenate all the vectors in a single Vector, sort it by value and iterate to call the function, but that makes me have to create a huge new vector, occupying new ram, and since the doThing will happen 60 times a second, if the vectors become big, it might be an overkill, i dont really want to create a new vector just to sort it, is there any other solution using the already existing vectors?

Its Java btw.

Could those be inserted into one vector at the beginning? They have to be maintained split up in separate vectors? — Grzegorz Piwowarek, Jul 07 '13 at 05:33
I am not sure what you are doing. You might have some thought that something is big on ram or there are many calculations; however, they might be small to your computer. Please provide us with more info of the problem/solution. — Multithreader, Jul 07 '13 at 05:43

score 1 · Answer 1 · edited May 23 '17 at 12:17

1

Premature optimizations are generally a bad idea.

Try the method that came to mind first: creating a giant ~~Vector~~¹ ArrayList and sorting it. If it turns out to be a performance issue, then you can start trying new things.

edited May 23 '17 at 12:17

Community

1
1

answered Jul 07 '13 at 05:40

Jeffrey

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To be honest there wasnt any performance drop, but since im trying to make it as perfect as I can i wanted to continue that direction instead of going for such a cheap solution on this "problem" =p Thank you for the tip – Xkynar Jul 07 '13 at 05:57

Stefan Haustein · Accepted Answer · 2013-07-07T06:00:59.467

If one, two and three are sorted, you could create an custom iterator that checks for a given set of lists what the smallest value at the current position is and proceed there.

Should look similar to this (not tested):

class MultiListIterator {
  List<Number>[] lists;
  int[] positions;

  MultiListIterator(List<Number>... lists) {
    this.lists = lists;
    positions = new int[lists.length];
  }

  boolean hasNext() {
    for (int i = 0; i < lists.length; i++) {
      if (positions[i] < lists[i].length) return true;
    }
    return false;
  }

  Number next() {
    int bestIndex = -1;
    Number bestNumber = null;
    for (int i = 0; i < lists.length; i++) {
      var p = positions[i];
      if (p >= positions[i].length) continue;
      Number n = lists[i].get(p);
      if (bestNumber == null || n.getValue() < bestNumber.getValue()) {
        bestIndex = i;
        bestNumer = n;
      }
    }
    if (bestNumber == null) throw new RuntimeException("next() beyond hasNext()");
    positions[bestIndex++];
    return bestNumber;
  }
}

Usage:

MultiListIterator mli = new MultiListIterator(one, two, three);
while (mli.hasNext()) {
  mli.next().doThing();
}

You may want to let MultiListIterator implement Iterator<Number>.

Note that Java already has a built-in class Number. Using the same name for your class might lead to a lot of confusion when you forget to import it somewhere.

It makes sense and since it is the actual answer to my question i accepted it, thank you =) — Xkynar, Jul 07 '13 at 05:58
Those classnames were invented for the question, i dont have any class named Number thanks for the warning though =p — Xkynar, Jul 07 '13 at 13:50

Calling function from several vectors ordered by element value

2 Answers2