Elixir Lists explained through q&a

This post works best when paired with the Elixir docs for a general overview of Lists.

What is an Elixir List?

A data type for storing a collection of values.

Are Lists in Elixir considered Linked Lists? What does that imply?

Yes. This means that when performing operations Elixir always begins with the first element in a List and ends with the last, another way of saying this is operations will run in linear time.

Is it faster to prepend or append a value to an Elixir List?


How do you add a value(s) to a List?

One way is by using the `|` operator to create a new List where the left hand side are the new values and the right hand side is the previous List. ``` => wise_words = ["battlestar galactical"] => ["bears", "beets" | wise_words] ["bears", "beets", "battlestar galactical"] ```

How do you merge one or more Lists into a single List?

Using the `++` operator. ``` => ["bears", "beets"] ++ ["battlestar galactical"] ["bears", "beets", "battlestar galactical"] => ["bears", "beets"] ++ ["battlestar galactical"] ++ ["boiled biscuits"] ["bears", "beets", "battlestar galactical", "boiled biscuits"] ```

How do you remove the first occurrence of a value from a List?

Using the `--` operator. See the example below: ``` => wise_words = ["bears", "beets", "beets", "battlestar galactical", "bears"] => wise_words -- ["beets", "bears"] ["beets", "battlestar galactical", "bears"] ```

How do you remove an element using its index?

Using the `List` modules `delete_at` method and providing an index as the second argument. The below removes the second element of the List: ``` => wise_words = ["bears", "beets", "battlestar galactical"] => List.delete_at(wise_words, 1) ["bears", "battlestar galactical"] ```

How do you remove the last Item from a List?

The below example uses the `Kernel` length function to get the index of the last element and then deletes that element using the `List.delete_at/2` function. ``` => wise_words = ["bears", "beets", "battlestar galactical"] => last_element_index = length(wise_words) - 1 => List.delete_at(wise_words, last_element_index) ["bears", "beets"] ```

What is the head of a List, what is the tail?

The head is the first element of a List and the tail is the rest of the Lists elements that follow.

How do you remove all elements with the same value from a List?

You can use the `Enum` module and the `filter` or `reject` functions. The following example removes all occurrences of "bears" and "beets" from the wise_words List. ``` wise_words = ["bears", "beets", "beets", "battlestar galactical", "bears"] Enum.filter(wise_words, fn (word) -> (word !== "bears") && (word !== "beets") end) ```

How do you retrieve the value of the head of a List? How do you retrieve the tail?

1. Using the `Kernel` modules `hd` and `tl` functions respectively: ``` => hd ["bears", "beets", "battlestar galactical"] "bears" => tl ["bears", "beets", "battlestar galactical"] ["beets", "battlestar galactical"] ``` 2. Using pattern matching: ``` => [head | tail] = ["bears", "beets", "battlestar galactical"] => head "bears" => tail ["beets", "battlestar galactical"] ```

More Elixir Decks:

  1. Atoms and Integers
  2. Tuples