A data structure is a way to store and organize data so that it can be used efficiently.

There are different kinds of data structures.

Two of the data structures we covered in the Python for Beginners course were lists and dictionaries.

lists - an ordered collection of items

dictionaries - an unordered collection of key:value pairs

Here is an example of a list and a dictionary:

# a list storing names names = ["Jim", "June", "Jake"] # a dictionary storing names and ages ages = { "Jim": 23, "June": 45, "Jake": 12, }

Alternative ways to store ages

Notice in the code example above that we are storing ages in a dictionary.

What if we had decided to store the ages in a list?

Or what if we had decided to store the ages in a dictionary but with the keys and values flipped?

As you can see there are different ways we can store the same data:

# option 1 ages = { "Jim": 23, "June": 45, "Jake": 12, } # option 2 ages = ["Jim", 23, "June", 45, "Jake", 12] # option 3 ages = { 23: "Jim", 45: "June", 12: "Jake", }

Now the question is which option should you choose?

Which option will be the most efficient?
Which option will use the least amount of memory?

The answer: it depends

Choosing the right data structure

Choosing the right data strcuture depends on what operations your program will be doing on that data structure.

Will your program primarily be inserting names and ages into the data structure?

Will your program primarily need to lookup the age of a person?

Will your program primarily need to sum all the ages of everyone and return the result?

Let's consider the lookup operation where a program will be given the name of a person and the program must return that person's age.

Depending on which data structure was chosen (option 1, 2 or 3) the sequence of steps to actually do a lookup operation will be different.

For example, here are the sequence of steps for looking up the age of "Jake" using the dictionary.

STEPS: 
Pass name into dictionary.
Save age to variable.

What are data structures and algorithms?