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Array, List, HashSet, and Dictionary are just four of the many collection types provided by the System.Collections.Generic namespace.
Array, list, hashSet and
dictionary can get us a long ways, but
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there are many other types of collections.
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All of them have specific advantages.
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It's important to always pick
the correct collection for
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the way the data is being used.
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The four collections
we've learned about so
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far may not always be the best for
the job.
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Let's briefly look at some of
the other less common collection
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types provided by the .NET Framework.
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We'll start in
the System.Collections.Generic namespace.
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Here we see another list collection.
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It's called LinkedList.
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LinkedList is different than the list
collection type we used earlier in
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this course.
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Linked lists are used when we
want to be able to quickly add or
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remove items without the items
in the list being shifted.
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This works because linked lists
don't use an array internally.
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Instead it's a list of individual
nodes that are linked to each other.
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They're much faster at adding and
removing items than an array based list.
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On the other hand, linked list
don't provide a quick way to index
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directly into items in
the list using an index.
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A queue is like a list except items can
only be added to the end of the queue and
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they can only be removed
from the beginning.
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This is why it's called a first in
first out or FIFO collection type.
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You can think of this just like
the line at a grocery store.
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The first person in the line is
the first person that checks out.
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A stack on the other hand is a last in,
first out or LIFO collection.
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With the stack we can only add and
remove items from one end of the stack.
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Think of this like a stack of plates.
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The last plate,
placed on the top of the stack,
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is the first one that'll be
used when we need a plate.
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Queues and stacks are limited in the types
of operations we can do with them, but
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these limitations allow them to be very
efficient at storing and retrieving data.
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They're commonly used to
simplify how algorithms for
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processing data are implemented.
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Then we have a number of
sorted collection types.
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A sortedSet doesn't use an object's hash
code to determine if it's in the set.
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Instead it keeps the items in the set
sorted, so they're arranged in
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such a way that it can quickly
determine if an item is in the set.
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Just like hashSet,
it also doesn't allow duplicates.
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SortedDictionary works
just like a sorted set,
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where the keys of
the dictionary are sorted.
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As with tne normal dictionary,
a value can be associated with each key.
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SortedSet and sortedDictionary take up
less additional memory than hashSet and
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the standard dictionary, especially
when the number of items becomes large.
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And of course they should be used if
we want to loop through the items or
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keys in a sorted order.
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SortedList is actually more like
a dictionary than it is a list.
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As you can see,
it contains both keys and values.
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Just like sortedDictionary, the keys of
a sorted list are stored in sorted order.
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It uses less memory than a sorted
dictionary but it's also slower adding and
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removing items.
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