Collections - LINQ functions

LINQ adds many extension methods to arrays, lists, strings and other collections. This recipe shows how to use some of them.

//create a collection (array) to use with other examples
var a = new string[] { "One", "Two", "Three", "Four", "Five" };

Get the first matching item. The callback function decides what items match; it can compare any property/condition/etc. This example looks for a string that starts with "F".

string s1 = a.FirstOrDefault(o => o.Starts("F"));
print.it(s1);

How it works: function FirstOrDefault calls the callback function (lambda) for each item until it returns true. Then FirstOrDefault returns that item.

Function FirstOrDefault returns null if not found. Function First throws exception instead. Function Any returns true/false. Function Count tells how many.

if (a.Any(o => o.Eqi("three"))) print.it("found"); else print.it("not found");
if (!a.Any()) print.it("the collection is empty");
int n1 = a.Count(), n2 = a.Count(o => o.Starts("F"));
print.it(n1, n2);

Function Where returns all matching items.

foreach (var v in a.Where(o => o.Starts("F"))) {
	print.it(v);
}

Many functions return a lazy IEnumerable object that may retrieve items later. Convert it to array or List if need.

string[] a2 = a
	.Where(o => o.Starts("F"))
	.ToArray(); //or ToList

Remove duplicate or similar elements.

var ai = new List<int> { 3, 4, 3, 5, 5, 1, 2, 1 };
print.it("Dictinct", ai.Distinct());
print.it("DictinctBy", a.DistinctBy(o => o[0])); //get strings with unique first character

Remove specified elements.

print.it("Except", ai.Except(new int[] { 1, 5 }));

Reverse.

print.it("reverse array", a.Reverse());
print.it("reverse string", "abc".Reverse());

Compare two collections.

var c1 = new int[] { 5, 2, 9 };
var c2 = new int[] { 5, 2, 9 };
var c3 = new int[] { 5, 3, 9 };
print.it(c1.SequenceEqual(c2), c1.SequenceEqual(c3));

Get elements that have/inherit the specified type.

var ao = new object[] { 3, "blue", 6.2, "yellow" };
print.it("strings", ao.OfType<string>());

Sorting.

print.it("sort", a.OrderBy(o => o));
print.it("sort descending, case-insensitive", a.OrderByDescending(o => o, StringComparer.OrdinalIgnoreCase));
print.it("sort by property", a.OrderBy(o => o.Length));

var at = new (int i, string s)[] { (5, "five"), (8, "eight"), (2, "eight") }; //array of tuples
print.it("sort by member", at.OrderBy(o => o.s));
print.it("sort by two members", at.OrderBy(o => o.s).ThenBy(o => o.i));

Transform elements from one type to other type.

print.it("Select: get a property", a.Select(o => o.Length)); //create ints from strings
print.it("Select: create objects of other type", a.Select(o => (o.Length, o))); //create tuples from strings