listremoveduplicates.md

List Remove Duplicates

Problem

Write a program (function!) that takes a list and returns a new list that contains all the elements of the first list minus all the duplicates.

Extras:

*Write two different functions to do this - one using a loop and constructing a list, and another using sets. *Go back and do Exercise 5 using sets, and write the solution for that in a different function.

Discussion

Concepts :

• Sets

Sets

In mathematics, a set is a collection of elements where no element is repeated. This becomes useful because if you know your data is stored in a set, you are guaranteed to have unique elements.

Features of sets

• Sets are not ordered. This means that there is no “first element” or “last element.” There are just “elements”. You cannot ask a set for it’s “next element”.
• There are no repeat elements in sets.
• You can convert between sets and lists very easily.

In Python

In Python, you make and use a set with the set() keyword. For example:

  names = set()
  names.add("Michele")
  names.add("Robin")
  names.add("Michele")
  print(names)

And the output will be;

  set(['Michele', 'Robin'])

You can do to a set almost anything you can do to a list (except ask for things like “the third element”). See the Python documentation about sets to get a full list of things you can do to sets.

You can convert from a list to a set and a set to a list pretty easily:

  names = ["Michele", "Robin", "Sara", "Michele"]
  names = set(names)
  names = list(names)
  print(names)

And the result of this will be:

  ['Michele', 'Robin', 'Sara']