How to sort a list of keyValuePair?

Question

The key is a GameObject and the value is a Vector3. The y and z axis are constant, so only the x changes. Based on t$$anonymous$$s, I want to sort them from left to right. Am understanding that I have to use a lambda expression to ac$$anonymous$$eve t$$anonymous$$s, but I don´t know what that is and am having a hard time figuring it out. Thanks in advance.

Answer 1

Answer by Bunny83 · Nov 01, 2022 at 09:49 PM

You never have to use a lambda expression. They just make it easier to write inplace anonymous methods.

So based on your descrption you have a

 List<KeyValuePair<GameObject, Vector3>> list;

w$$anonymous$$ch you want to sort based on the x value of the Vector3 value of each pair? You should be able to do t$$anonymous$$s:

 list.Sort((a, b) => a.Value.x.CompareTo(b.Value.x));

As I said, lambda expression are just in place shortcuts for anonymous methods. In addition they can be closures, but that' irrelevant here. You can instead use a method like t$$anonymous$$s

 private static int SortOnValueX(KeyValuePair<GameObject, Vector3> a,KeyValuePair<GameObject, Vector3> b)
 {
     return a.Value.x.CompareTo(b.Value.x);
 }

T$$anonymous$$s is the exact same method and can be used instead:

 list.Sort(SortOnValueX);

That's why lambda expressions are usually simpler.

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Feref2 · Nov 02, 2022 at 12:23 AM 0

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Thanks a lot for your reply. Could you please explain a little bit more this line of code? list.Sort((a, b) => a.Value.x.CompareTo(b.Value.x)); //What are a and b. Am assuming that a is an index for all keyValuePairs that are being compared against the current b...? or something? Sorry if it's a dumb question. It's probably obvious, but I don´t know.

Bunny83 Feref2 · Nov 02, 2022 at 02:14 AM 0

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I just gave you the equivalent normal method. I said:

This is the exact same method

So how do you come to the conclusion a and b would be indices? The Sort method uses the callback to sort the elements in the list. "a" and "b" are simply two elements from the list that should be compared. The method returns an integer value that should indicate if a should become before b or the other way round. This is indicated either by a positive or negative value. When the method returns 0, the two values are the same. The CompareTo method does exactly return such a value.

Again, look at the signature of the static method I posted above. The two arguments a and b have the type KeyValuePair<GameObject, Vector3>. It's simply the element type of your List

If you still have trouble I would recommend you start by reading the documentation of the Sort method. The Sort method has 4 overloads. We use the one that takes a Comparison<T> delegate. See the documentation of that delegate for more information.

This is just standatd C# and nothing Unity specific.

How to sort a list of keyValuePair?

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