How to use Linq to combine strings and lists?

Question

Novice linq user but prim_clus_list &ref_clus_list are a List and ref_clus & prim_clus are strings. I'm trying to do the following but it's not working.

string[] clus_list = prim_clus_list.Union(ref_clus_list).Union(ref_clus.ToList()).Union(prim_clus.ToList()).ToArray<string>();

How can I do this in one line? I want them all in one list with no duplicates.

CS1928: 'System.Collections.Generic.IEnumerable' does not contain a definition for 'Union' and the best extension method overload 'System.Linq.Queryable.Union(System.Linq.IQueryable, System.Collections.Generic.IEnumerable)' has some invalid arguments

Also this alone works fine:

string[] clus_list = prim_clus_list.Union(ref_clus_list).ToArray<string>();

If ref_clus is string, then ref_clus.ToList().ToList() shouldn't compile, unless you have extension methods for string — Fabio
– Fabio, Commented May 30, 2018 at 1:05
If you are novice then you should read documentation of linq, union and string first — Chetan
– Chetan, Commented May 30, 2018 at 1:05
@ChetanRanpariya - if we read documentation carefully, we don't need StackOverflow then :) — Fabio
– Fabio, Commented May 30, 2018 at 1:07

Fabio · Accepted Answer · 2018-05-30 01:23:45Z

2

Use .Append method to append single item to IEnumerable

var result = prim_clus_list.Append(ref_clus)
                           .Append(prim_clus)
                           .Union(ref_clus_list)
                           .ToArray();

Put Union in the end of the chain to get rid of duplicates.

Enumerable.Append(IEnumerable, TSource) Method

edited May 30, 2018 at 1:23

answered May 30, 2018 at 1:11

Fabio

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2 Comments

Enigmativity Over a year ago

I get an CS0023 Operator '.' cannot be applied to operand of type 'void' error when I try this code?

Enigmativity Over a year ago

My bad. I had a rogue extension method that was taking precedence.

Enigmativity · Accepted Answer · 2018-05-30 01:10:43Z

0

This is what you need:

var prim_clus_list = new List<string>() { "A", "B" };
var ref_clus_list = new List<string>() { "C", "D" };
var ref_clus = "E";
var prim_clus = "F";

string[] clus_list =
    prim_clus_list
        .Union(ref_clus_list)
        .Union(new [] { ref_clus })
        .Union(new [] { prim_clus })
        .ToArray<string>();

That gives:

A 
B 
C 
D 
E 
F

Basically ref_clus.ToList() returns a List<char>, but new [] { ref_clus } returns an IEnumerable<string> which can be used with .Union.

answered May 30, 2018 at 1:10

Enigmativity

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