LINQ select query data operator

Here are some operators that query data and then select the data again:

First-returns one element in the collection;

FirstOrDefault-Returns the first element in the collection (returns the default value if none);

Last-Returns the final element in the collection;

LastOrDefault-Returns the last element in the collection (default value if not)

ElementAt-Returns the element of the specified index in the collection;

Elementatordefault-Returns the element of the specified index in the collection (if not, returns the default value);

Contains-Determines whether a set contains an element;

Any-determines whether an element in the set satisfies a condition;

All-Determines whether all elements in the collection meet a certain condition;

Count-Returns the number of elements in the collection, returns an int;

LongCount-Returns the number of elements in the collection, returns a long;

Sum-The collection should be a collection of numeric types, and no delay

Min-Returns the minimum value of the collection;

Max-Returns the maximum value of the collection;

Average-The collection should be a collection of numeric types, averaging; no delay

Aggregate-Gets an aggregate value based on the input expression, without delay

Cast-Converts the collection to a strongly typed collection;

DefaultIfEmpty-The default value is returned when the query result is empty;

SequenceEqual-Determines whether two sets are the same;

OfType-Filters The specified type in the collection;

ToArray-Converts the collection to an array;

ToList-Converts the collection to a List<t> collection;

ToDictionary-Converts the collection to <k, v> collection;

LINQ select query data operator