Partitioning Operators: Take & TakeWhile

Partitioning operators split the sequence (collection) into two parts and returns one of the parts.

The Take() extension method returns the specified number of elements starting from the first element.

IList<string> strList = new List<string>(){ "One", "Two", "Three", "Four", "Five" };

var newList = strList.Take(2);

foreach(var str in newList)
    Console.WriteLine(str);

Take & TakeWhile operator is Not Supported in C# query syntax. However, you can use Take/TakeWhile method on query variable or wrap whole query into brackets and then call Take/TakeWhile().

Dim takeResult = From s In studentList
                 Take 3
                 Select s

TakeWhile

The TakeWhile() extension method returns elements from the given collection until the specified condition is true. If the first element itself doesn't satisfy the condition then returns an empty collection.

The TakeWhile method has two overload methods. One method accepts the predicate of Func<TSource, bool> type and the other overload method accepts the predicate Func<TSource, int, bool> type that passes the index of element.

In the following example, TakeWhile() method returns a new collection that includes all the elements till it finds a string whose length less than 4 characters.

IList<string> strList = new List<string>() { 
                                            "Three", 
                                            "Four", 
                                            "Five", 
                                            "Hundred"  };

var result = strList.TakeWhile(s => s.Length > 4);

foreach(string str in result)
        Console.WriteLine(str);

In the above example, TakeWhile() includes only first element because second string element does not satisfied the condition.

TakeWhile also passes an index of current element in predicate function. Following example of TakeWhile method takes elements till length of string element is greater than it's index

IList<string> strList = new List<string>() { 
                                            "One", 
                                            "Two", 
                                            "Three", 
                                            "Four", 
                                            "Five", 
                                            "Six"  };

var resultList = strList.TakeWhile((s, i) => s.Length > i);

foreach(string str in resultList)
        Console.WriteLine(str);