CODEWITHSUNDEEP
javasorting
lavhmrps
lavhmrps

Reputation: 21

What's the best way to sort some items in a list in one way, and the rest, another way?

Say I do a search which returns a list of objects

{ age: 5, color: Yellow, eggs: 2 }
{ age: 3, color: White,  eggs: 5 }
{ age: 4, color: Brown,  eggs: 9 }
{ age: 2, color: Green,  eggs: 4 }
{ age: 3, color: Red,    eggs: 1 }
{ age: 1, color: Blue,   eggs: 6 }

I would like to output them all, but in a particular order. If age is 3, I want these items first, sorted on most amount of eggs. Then I want the rest of the items sorted alphabetically on color.

So the sorted list would be 

|   3's: eggs   |    rest: alphabetically on color    |
 White  -  Red  -  Blue  -  Brown  -  Green  -  Yellow

What is the best way to do this sorting, preferably without creating temporary lists?

Can it be done using a single Comparator, or using streams maybe?

Upvotes: 1

Views: 62

Answers (2)

Jim Mischel
Jim Mischel

Reputation: 133975

You can do it with a single, kind of messy, Comparator. The idea is:

int compare(myType obj1, myType obj2)
{
    // first compare age
    if (obj1.age == 3)
    {
        if (obj2.age == 3)
        {
            // ages are both 3, so count eggs
            return obj1.eggs.compareTo(obj2.eggs);
        }
        // age 3 sorts before everything else
        return -1;
    }
    else if (obj2.age == 3)
    {
        // if obj2.age is 3, and obj1.age isn't 3,
        // then obj1 is greater than obj2
        return 1;
    }

    // compare color
    return obj1.color.compareTo(obj2.color);
}

Please excuse any syntactical mistakes; my Java is a bit rusty.

Upvotes: 1

stholzm
stholzm

Reputation: 3455

Since Java 8, Comparator has a few helpful static methods:

new AgeComparator().thenComparingInt(MyObj::getEggs).thenComparing(new ColorComparator());

Not sure what your class looks like - is that what you are asking for?

In general, I also like Apache Commons' CompareToBuilder for combining comparisions, but in your case it seems too limited.

Upvotes: 0

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