Determine If a Sequence Contains All Elements of Another Sequence Using Linq

Determine if a sequence contains all elements of another sequence using Linq

Count? How about Not Any?

bool contained = !subset.Except(superset).Any();

In C#, how can i determine if a list has any item from another list?

You're looking to see if the "Intersection" of the lists is non-empty:

if(list.Intersect(list2).Any())
    DoStuff();

LINQ: Determine if two sequences contains exactly the same elements

If you want to treat the arrays as "sets" and ignore order and duplicate items, you can use HashSet<T>.SetEquals method:

var isEqual = new HashSet<int>(first).SetEquals(second);

Otherwise, your best bet is probably sorting both sequences in the same way and using SequenceEqual to compare them.

Check if one IEnumerable contains all elements of another IEnumerable

There is no "fast way" to do this unless you track and maintain some state that determines whether all values in one collection are contained in another. If you only have IEnumerable<T> to work against, I would use Intersect.

var allOfList1IsInList2 = list1.Intersect(list2).Count() == list1.Count();

The performance of this should be very reasonable, since Intersect() will enumerate over each list just once. Also, the second call to Count() will be optimal if the underlying type is an ICollection<T> rather than just an IEnumerable<T>.

Check if enumeration contains multiple elements without throwing exception?

One approach to see if the sequence has more than one element is to use Take and Count, like this:

if (mySequence.Take(2).Count() == 2) {
    ... // Sequence has at least two elements
}

Take(2) limits counting to at most two, so using Count() is not as expensive as in mySequence.Count() > 1.

If you need to grab the first element, store the result of Take in a list to avoid iterating the sequence again.

Determine sequence contains no element using LINQ

Try

var d = lst1.Where(q => q <= DateTime.Now).DefaultIfEmpty().Max();

Your result will now contain DateTime.MinValue if there are no matches

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