# Sorting Two Arrays at a Time?

**URL:** <https://discourse.processing.org/t/sorting-two-arrays-at-a-time/5164>\
**Category:** Coding Questions\
**Created:** [November 3, 2018, 6:33pm UTC](https://discourse.processing.org/t/sorting-two-arrays-at-a-time/5164 "2018-11-03T18:33:57Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![alexac692](https://avatars.discourse-cdn.com/v4/letter/a/3be4f8/32.png) [@alexac692](https://discourse.processing.org/u/alexac692)\
**Post date:** [November 3, 2018, 6:33pm UTC](https://discourse.processing.org/t/sorting-two-arrays-at-a-time/5164/1 "2018-11-03T18:33:57Z")

</div>

My problem is that I want to take an array and “reassign” indices so that you can list them from lowest to highest, without actually shuffling the original array. In this case it’s with student IDs and I want to be able to print them from lowest to shortest, but without shuffling so I can preserve the link between the IDs and the other info. This is what I have:

```auto
void setup(){
               
int [] students_id= {10001, 20001, 12334, 14332, 99999, 10111, 20101, 12034, 10332, 99991} ;

int[] indices = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9};
sort_records_by_id(indices, students_id);
println(indices);

}

void sort_records_by_id (int []indices, int []students_id) {
  
  int [] id_copy = students_id;
  
  // start at the beginning of the list and work down...
  for (int k = 1; k < id_copy.length; k++)
  {
    //swap the lower value with the one above it until no
    // more swapping is needed or beginning of list is
    // reached
    for (int j = k; j > 0 && id_copy[j] < id_copy[j - 1]; j-- )
    {
      int place_holder_id = id_copy[j];
      id_copy[j] = id_copy[j-1];
      id_copy[j-1] = place_holder_id;
      
      int place_holder_i = indices[j];
      indices[j] = indices[j-1];
      indices[j-1] = place_holder_i;
    }
  }
     println(id_copy);
}

```

However, this program seems to sort the ID\_copy properly, but does not order the respective indices array properly. What am I doing wrong?

---

<div class="post-metadata">

**Author:** ![GoToLoop](https://yyz2.discourse-cdn.com/flex036/user_avatar/discourse.processing.org/gotoloop/32/86_2.png) [@GoToLoop](https://discourse.processing.org/u/GoToLoop)\
**Post date:** [November 3, 2018, 6:38pm UTC](https://discourse.processing.org/t/sorting-two-arrays-at-a-time/5164/2 "2018-11-03T18:38:49Z")

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Make a Student class w/ fields _id_ & _idx_:

```auto
class Student {
  int id, idx;

  Student(int ident, int ind) {
    id = ident;
    idx = ind;
  }
}

```

---

<div class="post-metadata">

**Author:** ![Jakub](https://yyz2.discourse-cdn.com/flex036/user_avatar/discourse.processing.org/jakub/32/2192_2.png) [@Jakub](https://discourse.processing.org/u/Jakub)\
**Post date:** [November 3, 2018, 10:37pm UTC](https://discourse.processing.org/t/sorting-two-arrays-at-a-time/5164/3 "2018-11-03T22:37:00Z")

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If I understand it correctly, you want to keep `students_id` without change, but sort the `indices` array based on the values in the `students_id` array.

To do that, in your sorting function, you need to use double indirection when comparing the values in the for loop condition, like this:

```auto
students_id[indices[j]] < students_id[indices[j - 1]]

```

Then you don’t need `id_copy` at all, you only swap values in the indices array as you are already doing.

Then you can print the student ids from lowest to highest like this:

```auto
println(student_ids[indices[0]]);
println(student_ids[indices[1]]);
...

```