How to sort multiple arrays in java

Question

I'm trying to sort three arrays by lexicographical order. The arrays are related to each other by a common array. It's easier to explain if I demonstrate:

int[] record = new int[4]; String [] colors = {"blue", "yellow", "red", "black"}; String [] clothes = {"shoes", "pants", "boots", "coat"}; 

When printed on the console, I would like them to be put in three columns similar to below:

Unsorted:

Record  Color   Clothes 0       blue    shoes 1       yellow  pants 2       red     boots 3       black   coat 

Sorted by Color:

Record  Color   Clothes 3       black   coat 0       blue    shoes 2       red     boots 1       yellow  pants 

Sorted by Clothes:

Record  Color   Clothes 2       red     boots 3       black   coat 1       yellow  pants 0       blue    shoes 

I found a previous answer similar to my scenario, but it compared integers instead of strings, and I'm having trouble using the compareTo() method and Arrays.sort() to arrive at my desired output.

Any help would be appreciated!

Answer 1

In some cases it doesn't make much sense to create a new class just to do sorting.

Here, is a function that can be used to sort an any number of arbitrarily typed lists (List<?>) based on a key list (List<T implements Comparable>). Ideone Example here.

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Usage

Here is an example of how you can use the function to sort multiple lists of arbitrary types:

List<Integer> ids = Arrays.asList(0, 1, 2, 3); List<String> colors = Arrays.asList("blue", "yellow", "red", "black"); List<String> clothes = Arrays.asList("shoes", "pants", "boots", "coat");  // Sort By ID concurrentSort(ids, ids, colors, clothes);  // Sort By Color concurrentSort(colors, ids, colors, clothes);  // Sort By Clothes concurrentSort(clothes, ids, colors, clothes); 

Output:

// Sorted By ID: ID:      [0, 1, 2, 3] Colors:  [blue, yellow, red, black] Clothes: [shoes, pants, boots, coat]  // Sorted By Color: ID:      [3, 0, 2, 1] Colors:  [black, blue, red, yellow] Clothes: [coat, shoes, boots, pants]  // Sorted By Clothes: ID:      [2, 3, 1, 0] Colors:  [red, black, yellow, blue] Clothes: [boots, coat, pants, shoes] 

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Code

An Ideone Example can be found here which includes validation of parameters and a test case.

public static <T extends Comparable<T>> void concurrentSort(                                         final List<T> key, List<?>... lists){     // Create a List of indices     List<Integer> indices = new ArrayList<Integer>();     for(int i = 0; i < key.size(); i++)         indices.add(i);      // Sort the indices list based on the key     Collections.sort(indices, new Comparator<Integer>(){         @Override public int compare(Integer i, Integer j) {             return key.get(i).compareTo(key.get(j));         }     });      // Create a mapping that allows sorting of the List by N swaps.     // Only swaps can be used since we do not know the type of the lists     Map<Integer,Integer> swapMap = new HashMap<Integer, Integer>(indices.size());     List<Integer> swapFrom = new ArrayList<Integer>(indices.size()),                   swapTo   = new ArrayList<Integer>(indices.size());     for(int i = 0; i < key.size(); i++){         int k = indices.get(i);         while(i != k && swapMap.containsKey(k))             k = swapMap.get(k);          swapFrom.add(i);         swapTo.add(k);         swapMap.put(i, k);     }      // use the swap order to sort each list by swapping elements     for(List<?> list : lists)         for(int i = 0; i < list.size(); i++)             Collections.swap(list, swapFrom.get(i), swapTo.get(i)); } 

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NOTE: The running time is O(mlog(m) + mN) where m is the length of the list and N is the number of lists. Usually m >> N so the running time is not more significant than sorting only the key O(mlog(m)).