C# LINQ in the wild

Find the duplicates in the list

Use GroupBy and Count

var query = lst.GroupBy(x => x)
              .Where(g => g.Count() > 1)
              .Select(y => y.Key)
              .ToList();

Query list that contains a list

https://stackoverflow.com/questions/2364090/linq-query-list-contains-a-list

ListObjectB.Where(p => p.ListOfObjectA.Any(x => ListOfIdsA.Contains(x.Id)))
ListObjectB.Where(p => p.ListOfObjectA.All(x => ListOfIdsA.Contains(x.Id)))

Distinct, ignoring case

Use StringComparer (https://stackoverflow.com/questions/283063/linq-distinct-operator-ignore-case)

private static List<string> GetDomains(IList<DomainService> services)
{
    return services
        .Select(x => x.Domain)
        .Distinct(StringComparer.OrdinalIgnoreCase)
        .OrderBy(x => x)
        .ToList();
}

Flatten queries, returning list of lists

https://stackoverflow.com/questions/958949/difference-between-select-and-selectmany

var releases = bankingCore.DeploymentGroups
    .Where(x => x.ReleaseDefinitions != null)
    .SelectMany(x => x.ReleaseDefinitions)
    .ToList();
var builds = bankingCore.DeploymentGroups
    .Where(x => x.BuildDefinitions != null)
    .SelectMany(x => x.BuildDefinitions)
    .ToList();