列表中的分区键<keyvaluepair> c#</keyvaluepair>

Question

I have a List of KeyValuePairs

var hitCoord = new List<KeyValuePair<int, double>>()

and sorted like this (descending by Key)

hitCoord.Sort((a, b) => (b.Key.CompareTo(a.Key)));

I can find the total highest Value with

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

(^ maybe that can be used for the following query?)

I would like to partition the Keys in my list such that I can find Values that meet a condition within the specified range of keys.

ie I would like to find the highest Value and Lowest Value in a range of (int)Keys

for (i=0; i<hitCoord.Count; i++)
{
     if (hitCoord[i].Key > (int lowerbound) && hitCoord[i].Key < (int upperBound)
     {
          find highest Value?
     }
}

Not sure if that is at all on the right track. I am new to programming and very new to KeyValuePairs. Any help you can offer on this matter is much appreciated! Thank you!

Answer 1

You don't need to actually sort - you can do this with Linq (adding using System.Linq; to the top of your.cs file). You just want a Where to filter by key and a Max to get the highest value:

var maxValue = hitCoord.Where(hc => hc.Key > lowerbound && hc.Key < upperBound)
                       .Max(hc => hc.Value);

Answer 2

Finding the max value in a specified range of keys could be solved by using LINQ ( using System.Linq; ) like this:

hitCoord.Where(c => c.Key > lowerbound && c.Key < upperbound).Max(c => c.Value);

The approach:

1. Use Where to filter all items with key in range
2. Use Max to get the max value

You could adapt and extend the query also with more checks and constraints. Some basic queries are described in Basic LINQ Query Operations (C#) .

Answer 3

As others have suggested this is all pretty easy to do with linq. here's another sample of linq calls including how to create a partition lookup.

var hitCoord = new List<KeyValuePair<int, double>>()
{
    new KeyValuePair<int, double>(1, 1.1),
    new KeyValuePair<int, double>(1, 1.2),
    new KeyValuePair<int, double>(2, 2.0),
    new KeyValuePair<int, double>(2, 2.1)
};

var partitions = hitCoord.ToLookup(kvp => kvp.Key % 2);

var maxKvp = hitCoord.Max(kvp => kvp.Key);
var minKvp = hitCoord.Min(kvp => kvp.Key);

int lower = 1;
int higher = 2;

var maxInRange = hitCoord.Where(kvp => kvp.Key >= lower && kvp.Key <= higher).Max(kvp => kvp.Key);

That said if this is perfromance critical then you'll probably want to use something other than linq so you can optimize it and avoid going through the list multiple times.