How to find key in Dictionary by using Linq

Question

I have a dictionary DateTime, DataTable

Key Values

2019/07/01 Column A | B

                  1 | 1

2019/07/02 Column A | B

                  3 | 4

2019/07/03 Column A | B

                  5 | 4

I would like to use linq to find the key of the dictionary with maximum value of column A in the dict.

In above case, my expected result is "2019/07/03"

I am new in linq. Is it possible for above use? How to do?

what is the key, what is the value? can you post dictionary definition? — cdev, Jul 26 '19 at 07:20
`dict.OrderByDescending(x => x.Value.A).FirstOrDefault()?.Key` — Slava Utesinov, Jul 26 '19 at 07:22
Please post this as a [mcve] to help people help you and get quicker and better answers. — Gert Arnold, Jul 26 '19 at 07:40
Possible duplicate of [How to use LINQ to select object with minimum or maximum property value](https://stackoverflow.com/questions/914109/how-to-use-linq-to-select-object-with-minimum-or-maximum-property-value) — Bruno Belmondo, Jul 26 '19 at 07:42

score 1 · Accepted Answer · answered Jul 26 '19 at 07:34

While .OrderByDescending(x=> x.Key).FirstOrDefault()?.Key; will give you the correct answer, it will result in first sorting the values which is time and memory inefficient.

What you want to do is scan all your values once without memory consumption:

 KeyValuePair<MyKey, MyValue> maxKey;
 if (list.Count > 0)
 {
    maxKey = list.Aggregate(list.First(), (first,second)=>first.Value.A>second.Value.A?first:second);
 }

score 0 · Answer 2 · answered Jul 26 '19 at 07:43

Another one example.

Dictionary<DateTime, int> example = new Dictionary<DateTime, int>() 
            { 
                {new DateTime(2019,07,01), 1 },
                {new DateTime(2019,07,02), 2 },
                {new DateTime(2019,07,03), 3 }
            };
var HighestKey = example.Keys.Max();

score -1 · Answer 3 · edited Jul 26 '19 at 07:35

-1

Please try below solution, I am sure it will work.

<DictionaryName>.OrderByDescending(x => x.Key).First();

edited Jul 26 '19 at 07:35

deHaar

11,298
10
32
38

answered Jul 26 '19 at 07:30

Ninad

1
2

If the dictionary is empty, this code would throw an exception. – Mark Cilia Vincenti Jul 26 '19 at 12:32

How to find key in Dictionary by using Linq

3 Answers3