using System.Collections.Generic;

using System.Linq;

using Xunit;

using Microsoft.VisualStudio.TestTools.UnitTesting;

​

public sealed class Variable {

    public string Name { get; }

​

    public Variable(string name) {

        Name = name;

    }

}

​

public static class VariableCollectionExtensions {

    public static IEnumerable<string> GetUniqueNames(this IEnumerable<Variable> variables) {

        var names = variables.Select(v => v.Name.Split('-').First()).ToList();

        return names?.Distinct().OrderBy(n => names.IndexOf(n));

    }

}

​

public class Program {

    [Fact]

    public static void Main() {

        var variables = new[] { new Variable("var1-1"), new Variable("var2"), new Variable("var1-2") };

        var expected = new[] { "var1", "var2" };

        var actual = variables.GetUniqueNames().ToList();

        CollectionAssert.AreEqual(actual, expected);

    }

}