Remap Lookup keys in C# using LINQ

Question

I have my Lookup looking like this:

Lookup<string, DataModel> lookup;

Besides that I have dictionary containing key mappings:

Dictionary<string, KeyModel> keyMappings;

What I want to do is to re-map string keys in lookup to the KeyModel entities in the following way:

Lookup    <string, DataModel> lookup;
             ||
             ||
Dictionary<string, KeyModel> keyMappings;
            ___________|
           v
Lookup<KeyModel, DataModel> result; 

Answer 1

Given:

Dictionary<string, KeyModel> keyMappings = ...;
ILookup<string, DataModel> lookup = ...;

the response is:

ILookup<KeyModel, DataModel> lookup2 = lookup
    .SelectMany(x => x, (grouping, element) => new { Key = keyMappings[grouping.Key], Element = element })
    .ToLookup(x => x.Key, x => x.Element);

So you first re-linearize the ILookup<,> by using SelectMany , and then recreate the ILookup<,> .

Clearly you need your KeyModel to define the GetHashCode() and the Equals() , or you need an IEqualityComparer<KeyModel> to pass as the parameter of the ToLookup()

Answer 2

You can use a simple foreach -loop.

First you need to transform your Lookup into a Dictionary. See here .

foreach (KeyValuePair<string, DataModel> kvp in lookup) {
KeyModel outValue;
if (keyMappings.TryGetValue(kvp.Key, out outValue))
{
    result.Add(outValue, lookup[kvp.Key]);
}}

Not the fastest solution, maybe someone is coming up with a nice LINQ.