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Sorting List<> in Java


By : Ashok
Date : September 14 2020, 08:00 PM
around this issue Java 8 introduced a sort method in the List interface which can use a comparator.
If you have a getter for secondName you can do this:
code :
 myList.sort(Comparator.comparing(Person::getSecondName));
myList.sort(Comparator.comparing((person)->(person.secondName)));


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sorting a List<List<Integer>> using java Collections.sort()


By : C.Varys
Date : March 29 2020, 07:55 AM
This might help you You'll need to implement a Comparator to sort custom data-structures like the one you provided.
code :
import static java.util.Arrays.asList;

List<List<Integer>> matchedPostions = asList(asList(1, 198, 200), asList(2, 50, 61));
Collections.sort(matchedPostions, new Comparator<List<Integer>>() {
    @Override
    public int compare(List<Integer> o1, List<Integer> o2) {
        // Sort the lists using the starting position (second element in the list)
        return o1.get(1).compareTo(o2.get(1));
    }
});

System.out.println(matchedPostions);
// [[2, 50, 61], [1, 198, 200]]

List iteration throws ConcurrentModificationException in Java 8 when sorting already sorted list


By : Joch
Date : March 29 2020, 07:55 AM
Any of those help My solution was twofold, either one would have worked. First of all, I moved the sorting away from the retrieve function so I wouldn't waste time - instead I moved it to the load function where it should have been in the first place. Secondly, in a lesser used function that returned the same list but sorted differently, I just created a new list, which I then sorted and returned:
code :
result = new ArrayList(oldList);
Collections.sort(result, otherComparator);
result = (result==null) ? null : Collections.unmodifiableList(result);

Sorting a list of lists by the first element of inner list (Java or groovy)


By : rodica
Date : March 29 2020, 07:55 AM
around this issue I have a list which contains a list of strings like so... , In groovy:
code :
list.sort { it[0][0] }
list.sort(false) { it[0][0] }

Java collections: Sorting a list of values according to a separate list of keys


By : user2455068
Date : March 29 2020, 07:55 AM
With these it helps If, as you say, you need to keep both lists, you could try something like the following:
code :
// Create a map that orders its data.
Map<Integer, String> tmp = new TreeMap<>();

// Put your data into this structure and let it sort the data for you.
for (int i=0; i<keys.size(); i++) {
    tmp.put(keys.get(i), values.get(i));
}

// Clear your original lists.
keys.clear()
values.clear();

// Put the data back into your lists - but sorted this time.
for (Integer key : tmp.keySet()) {
    keys.add(key);
    values.add(tmp.get(key));
}

Sorting a List of integers based on a List of strings in Java


By : user3053722
Date : March 29 2020, 07:55 AM
wish helps you You can further specialize the compareTo function to enact a secondary comparison. I'm assuming that every list contains at least one country; if such is not the case, you must handle empty lists. The altered compareTo is as so:
code :
@Override
public int compareTo(Wonder other) {
    if(this == other) {
        return 0;
    } else if(hostility < other.hostility) {
        return -1;
    } else if(hostility > other.hostility) {
        return 1;
    } else {
        return -countries.get(0).compareTo(other.countries.get(0));
    }
}
wonders.sort(Comparator.comparingInt(Wonder::getHostility).reversed()
    .thenComparing(wonder -> wonder.getCountries().get(0)));
//don't reverse afterwards!
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