# Take

# Usage

C# offers the .Take() extension method which, as its name implies, takes the first 'n' elements from a collection.

Take method:

• returns a specified number of elements from the start of a collection.
• it returns an IEnumerable<T> that contain the elements specified as above.
• if the parameter is less than or equal to zero, an empty IEnumerable<T> is returned.

# How to take the first 'n' items from a collection?

var numbers = new List<int> { 2, 32, 11, 1, 24, 7 };
var top = 3;

var firstNumbers = numbers
    .Take(top);

But this is not memory-efficient due to the fact that through the .Take() method the compiler creates in memory a new collection and returns it.

We can avoid that by chaging the logic: instead of using the .Take() method, we can operate on the input collection by removing the elements whose index exceeds the 'top' value.

In this way, our collection will contain only the first 'top' items.

But, I need to make a remark. We cannot use 'for' loop like this:

for (var i = top; i < numbers.Count; i++)
{
    numbers.RemoveAt(top);
}

Why? Well because as you remove, the number of items in the list shrinks and the collection.Count() will also shrink and you end up having more elements because the i indexer is still growing when you remove items.

So, here are three ways of how to do this; preferably choose the first one:

1. by using a 'while' loop:

while (numbers.Count != top)
{
    numbers.RemoveAt(top);
}

2. by keeping the length unchanged:

var end = numbers.Count;
for (var i = top; i < end; i++)
{
    numbers.RemoveAt(top);
}

3. by not incrementing the indexer:

for (var i = top; i < numbers.Count; i++)
{
    numbers.RemoveAt(i);
    i--;
}

# Differed execution

This method returns a query which is not executed until you call GetEnumerator or loop through it with a foreach.