How to sort List of Array by two fields

Bob :

I have List of Double Array and I would like sort it according to first and last field. So far I am able to sort it by only 1 element of array.

Real state:

0         1         2
-------  -------  -------
78       100        0
78       100        1
0        100        0
104      100        1

Expected:

0         1         2
-------  -------  -------
0        100       0
78       100       1
78       100       0
101      100       1

I want to sort field according to value of 1st element of Array. If value of 1st and 2nd are equal I want to sort according to 3rd element where first should be 1 and then 0 (there will be only 1 and 0 value)

List<Double[]> splitList = new ArrayList<>();
Double[] tmp1 = { 78d, 100d, 0d };
Double[] tmp2 = { 78d, 100d, 1d };
Double[] tmp3 = { 0d, 100d, 0d };
Double[] tmp4 = { 104d, 100d, 1d };
splitList.add(tmp1);
splitList.add(tmp2);
splitList.add(tmp3);
splitList.add(tmp4);
splitList.sort(Comparator.comparingDouble(a -> a[0]));

This one sort me according to first element. I found solution to sort by two elements https://stackoverflow.com/a/26865122/9774735 so I tried it:

splitList.sort(Comparator.comparingDouble(a -> a[0]).thenComparingDouble(b -> b[2]));

and it output me an error:

Multiple markers at this line
    - The type of the expression must be an array type but it resolved 
     to Object
    - The type of the expression must be an array type but it resolved 

How can I compare List of Array?

Lino :

Seems like the java compiler has problems in infering the generic type, you have some options to overcome this problem:

1. Use type hints with the pattern Class.<GenericType>.method(Arguments):

   splitList.sort(Comparator.<Double[]>comparingDouble(a -> a[0]).thenComparingDouble(b -> b[2]));
   

2. Declare the lambda parameter type (declaring it for the first seems to be enough):

   splitList.sort(Comparator.comparingDouble((Double[] a) -> a[0]).thenComparingDouble(b -> b[2]));
   

After reading your comments you want to reverse the last comparison, which can be done like this:

Comparator.<Double[]>comparingDouble(a -> a[0])
   .thenComparing(Comparator.<Double[]>comparingDouble(b -> b[2]).reversed())

Which is quite messy, you're better of using something like this:

splitList.sort((a, b) -> {
    int c = Double.compare(a[0], b[0]);
    return c == 0 ? Double.compare(b[2], a[2]) : c;
});