Sorting array of Strings based on array of Doubles

Question

So, I want to sort descending the array of doubles, and, accordingly to sort my array of strings. Both of my arrays have the same length.

This is how i do it (adapted from another answer in here):

arrayS contains the strings and array contains the doubles.

List<String> stringList = Arrays.asList(arrayS);
Collections.sort(stringList, Comparator.comparing(s -> array[stringList.indexOf(s)]));

I am getting out of bounds error on the second line.

More info:

System.out.println("arrayS: "+arrayS.length+" array: "+array.length);

out -> arrayS: 125 array: 125

Java is an Object-Oriented Language. Use it. Don't use parallel arrays. Define a new class with the two values as fields, then have a single array of those objects. Now the double and the String values are always paired, so when you sort the array, all is good. — Andreas
– Andreas, Commented Mar 10, 2017 at 21:48
Btw, sorting stringList will also sort the underlying arrayS. If that's your intent, you can just sort it directly using Arrays.sort(). — shmosel
– shmosel, Commented Mar 10, 2017 at 21:57

shmosel · Accepted Answer · 2017-03-10 21:36:35Z

3

You're searching for the elements while the list/array is being sorted. That's a recipe for disaster. You need to use one list for index reference and another for sorting:

List<String> stringList = Arrays.asList(arrayS);
List<String> indexes = new ArrayList<>(stringList);
Collections.sort(stringList, Comparator.comparingDouble(s -> array[indexes.indexOf(s)]));

answered Mar 10, 2017 at 21:36

shmosel

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7 Comments

shmosel Over a year ago

@Mp.Lo. I'm not sure how you're testing, but it works fine for me: ideone.com/jYE3MC

Jérôme Over a year ago

Just a small remak: You can directly use stringList.sort(...) no need for Collections.sort(...). The code works for me too.

Mp. Lo. Over a year ago

@shmosel I think the output is correct, but when i print the array of double it looks unsorted. But the array of strings looks sorted. hmm i dont get this.

shmosel Over a year ago

@Mp.Lo. Why would the double array be sorted? If you want to sort it, you'll have to to so separately: Arrays.sort(array);

Mp. Lo. Over a year ago

Cheers, the thing is that these java shortcuts although they work really nicely, they are pretty 'hard' for novice users to comprehend.

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