Find closest value in a list in C# with linq?

Question

I've a list like this:

public List<Dictionary<int, int>> blanks { get; set; }

This keep some index values:

In addition I have also a variable named X. X can take any value. I want to find closest 'Key' value to X. For example:

If X is 1300, I want to take blanks index: 2 and Key: 1200. How can I do this via linq? Or, is there any other solution?

Thanks in advance.

EDIT: What if it is not a Dictionary. What if it is a List like this:

List<List<int[]>> lastList = new List<List<int[]>>();

This time, I want to take first List's indexes and second List's index. For example, if X is 800, I want to take 0 and 0 (for index 0) and also take 1 and 1 (for index 1) How can I do this time?

Answer 1

var diffs = blanks.SelectMany((item, index) => item.Select(entry => new
            { 
              ListIndex = index, // Index of the parent dictionary in the list 
              Key = entry.Key, // Key
              Diff = Math.Abs(entry.Key - X) // Diff between key and X
            }));

var closestDiff = diffs.Aggregate((agg, item) => (item.Diff < agg.Diff) ? item : agg);

Dictionary<int, int> closestKeyDict = blanks[closestKey.ListIndex];
int closestKey = closestDiff.Key;
int closestKeyValue = closestKeyDict[closestKey];

The SelectMany clause flattens all the dictionaries entries into a collection of { ListIndex, DictionaryKey, Difference } instances.

This flattened collection is then aggregated to retrieve the item with the minimum difference.

To answer your second questsion:

var diffs = blanks.SelectMany((list, listIndex) => list.
                   SelectMany((array, arrayIndex) => array.
                   Select((item, itemIndex) => new
                   { 
                     ListIndex = listIndex,
                     ArrayIndex = arrayIndex,
                     ItemIndex = itemIndex,
                     Diff = Math.Abs(item - X) 
                   })));

var closestDiff = diffs.Aggregate((agg, item) => (item.Diff < agg.Diff) ? item : agg);

Now in closestDiff you'll find the indices of the closes item (List index, array index and array item index)

Answer 2

This might not be the most optimized way but it should just work,

List<Dictionary<int, int>> blanks = new List<Dictionary<int, int>>
{
    new Dictionary<int, int>{{100,200}},
    new Dictionary<int, int>{{500,200}},
    new Dictionary<int, int>{{700,200}},
    new Dictionary<int, int>{{1200,200}},
    new Dictionary<int, int>{{300,200}},
    new Dictionary<int, int>{{200,200}},
    new Dictionary<int, int>{{800,200}},
};

int x = 1300;

IEnumerable<int> keys = blanks.SelectMany(ints => ints.Keys);
var diff = keys.Select(i => Math.Abs(i - x)).ToList();
var index = diff.IndexOf(diff.Min());
var value = blanks[index].Keys.First();