How to sort the string number in descending order?

Question

Below is my list which will always be in the form of bXXXX -

List<String> data = Arrays.asList("b5", "b10", "b2", "b1", "b40");
System.out.println(data);

My data list will always have strings in the form of bXXXX

Now I need to sort my above lists in descending order and extract the largest string from it..

So in the above example, it will be b40.. So below is the comparator I am using which sorts everything in ascending order -

static final Comparator<String> aStringComparator = new Comparator<String>() {
    public int compare(String s1, String s2) {
        //assumed input are strings in the form axxxx
        int numfromS1 = Integer.valueOf(s1.subSequence(1, s1.length()).toString());
        int numfromS2 = Integer.valueOf(s2.subSequence(1, s2.length()).toString());
        return numfromS1 - numfromS2;
    }
};

And I am not able to understand how do I make this to sort it out in descending order so that I can extract the first index from the list which will be greatest string number?

Answer 1

If your comparator works in ascending order, then all you need to do is to invert the result of your comparator.

If this code works for you:

return numfromS1 - numfromS2;

then change it to:

return numfromS2 - numfromS1;

or, maybe to the little more idiomatic:

return (numfromS2 < numfromS1) ? -1: (numfromS2 > numfromS1) ? 1 : 0;

and now your data is going to be in descending order.

You could also, as suggested by others, use either:

return ((Integer) numfromS2).compareTo(numfromS1);

or:

Collections.sort(data, Collections.reverseOrder(aStringComparator));

Answer 2

Use this to sort in descending order -

Collections.sort(data, Collections.reverseOrder(aStringComparator));

Answer 3

Try this:

    Collections.sort(data, new Comparator<String>() {
        @Override
        public int compare(String s1, String s2) {
            int n1 = Integer.parseInt(s1.substring(1));
            int n2 = Integer.parseInt(s2.substring(1));
            return Integer.compare(n2, n1);
        }});

Answer 4

def Descending_Order(num): > # num = 18902

l = list(map(int, str(num)))            >  # [1, 8, 9, 0, 2]

r = sorted(l,reverse=True)              > # [9, 8, 2, 1, 0]

ch_r = map(str, r)                      > # ['9', '8', '2', '1','0']

num_r =''.join(ch_r)                    > # '98210'

return int(num_r)                       > # 98210