Add unit for removing elements from Array

Author: paulgoetze

4_Arrays/4_Removing_elements/solution.rb

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+baggage = ['shoes', 'underwear', 'socks', 'kettle', 'glasses', 'shirt', 'wallet']
+
+baggage.shift
+baggage.delete('kettle')
+baggage.pop
+
+# baggage
+# => ["underwear", "socks", "glasses", "shirt"]

4_Arrays/4_Removing_elements/solution_spec.rb

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+require 'rspec'
+require 'code_breaker'
+
+describe 'Your code' do
+  [['solution::code']]
+
+  VARIABLE = :baggage
+  ITEMS    = ['shoes', 'underwear', 'socks', 'kettle', 'glasses', 'shirt', 'wallet']
+
+  it 'defines a variable with name "baggage"' do
+    expect(local_variables.include?(VARIABLE)).to be true
+  end
+
+  if local_variables.include?(VARIABLE)
+    before(:all) do
+      @statements = CodeBreaker.parse(%q{ [['solution::code']] })
+    end
+
+    it 'uses the shift method to remove "shoes"' do
+      shift = [{ lvar: VARIABLE }, :shift]
+      expect(@statements.include?(shift)).to be true
+    end
+
+    it 'uses the delete method to remove the "kettle"' do
+      delete = [{ lvar: VARIABLE }, :delete, String]
+      expect(@statements.include?(delete)).to be true
+    end
+
+    it 'uses the pop method to remove the "wallet"' do
+      pop = [{ lvar: VARIABLE }, :pop]
+      expect(@statements.include?(pop)).to be true
+    end
+
+    it 'changes your baggage to only contain "underwear", "socks", "glasses", & "shirt"' do
+      expect(eval(VARIABLE.to_s)).to eq ['underwear', 'socks', 'glasses', 'shirt']
+    end
+  end
+end

4_Arrays/4_Removing_elements/task.md

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+# Removing elements from Arrays
+
+---
+
+*You will learn:*
+- how to remove elements from the end of an Array
+- how to remove elements from the beginning of an Array
+- how to remove elements from an Array after a specific index
+- how to remove a specific element
+
+---
+
+Once you have created an Array, there might be the case that you don’t want to keep
+all of the Array’s elements. This is where some methods for removing elements come
+in handy.
+
+This unit will look into different ways of removing elements from an Array.
+
+## Removing elements from the end of an Array
+
+For removing one ore more elements from the end of an Array you can use the `pop`
+method. The `pop` method modifies the orginal Array and returns the removed elements.
+You can pass the number of elements to remove as argument:
+
+`  numbers = [1, 2, 3, 4]`
+`  numbers.pop(2)`        *# => [3, 4]*
+`  numbers`               *# => [1, 2]*
+
+If you don’t pass the number of elements it will delete one element by default:
+
+`  numbers = [5, 6, 7, 8]`
+`  numbers.pop`             *# => 8*
+`  numbers`                 *# => [5, 6, 7]*
+
+Note that, if you remove multiple elements, `pop` will return an Array with the removed
+elements. If you just remove the last element it will return this element.
+
+If you try to pop an element from an empty Array, there’s no element left to remove
+and it will return *nil*:
+
+`  [].pop`                  *# => nil*
+
+## Removing elements from the beginning of an Array
+
+For removing elements from the beginning of an Array you can use the `shift` method.
+It takes an optional argument that specifies the number of elements to remove:
+
+`  numbers = [0, 1, 2, 3]`
+`  numbers.shift(3)`        *# => [2, 3]*
+`  numbers`                 *# => [0, 1]*
+
+If you don’t pass an argument it will only remove and return the very first element:
+
+`  numbers = [2, 4, 6]`
+`  numbers.shift`           *# => 2*
+`  numbers`                 *# => [4, 6]*
+
+Similar to `pop`, `shift` will return *nil* if it is called on an empty Array:
+
+`  [].shift`                *# => nil*
+
+## Removing elements after a specific index
+
+There might be situations where you want to select all elements of an Array after
+a certain position, e.g. all elements after the third element.
+You can do this with the `drop` method:
+
+`  fruits = ['apple', 'pear', 'lemon', 'melon']`
+`  fruits.drop(2)`          *# => ["lemon", "melon"]*
+`  fruits`                  *# => ["apple", "pear", "lemon", "melon"]*
+
+In contrast to `pop` and `shift`, `drop` does not modify the original Array but 
+creates a new Array that comprises the dropped elements.
+
+## Removing specific elements
+
+In case you know the elements in an Array, you can specificly remove these.
+There are two similar methods for doing this: `delete` and `-`.
+
+The difference is, that `delete` modifies the original Array, while `-` creates a new
+Array and does not change the original Array.
+
+`delete` takes the element that should be removed from the Array and returns the
+removed element:
+
+`  fruits = ['apple', 'lemon', 'lemon']`
+
+`  fruits.delete('lemon')`  *# => "lemon"*
+`  fruits`                  *# => ["apple"]*
+
+As you can see, `delete` removes duplicated elements from the Array, here all the
+*'lemon'* elements.
+
+The `-` method takes an Array as argument. It also removes duplicated elements:
+
+`  fruits = ['apple', 'lemon', 'lemon', 'melon']`
+
+`  less_fruits = fruits - ['lemon']` *# => ["apple", "melon"]*
+`  fruits`                           *# => ["apple", "lemon", "lemon", "melon"]*
+
+The `-` does not modify the original Array but creates a new one. The original
+Array that is stored in *fruits* remains the same.
+
+Before going to this unit‘s task, let’s summarize all the learned methods for removing
+elements from an Array:
+
+`  pop`     *removes elements at end            modifies the original Array*
+`  shift`   *removes elements at beginning      modifies the original Array*
+`  drop`    *remove elements after given index  creates a new Array*
+`  delete`  *removes the given element          modifies the original Array*
+`  -`       *removes the given elements         creates a new Array*
+
+---
+
+Let’s use our baggage again and unpack a couple of things.
+Define a variable *baggage* and assign an array with all the things you want to
+take with you: *shoes*, *underwear*, *socks*, *kettle*, *glasses*, *shirt*, and *wallet*.
+
+You just realized, that you actually want to wear your *shoes* (which are the first
+thing in your baggage), so remove them from your *baggage*.
+
+Your friend tells you that you won’t need the *kettle*, so delete it from your *baggage*, too.
+
+Last, you think that it’s maybe a better idea to carry your *wallet* with you.
+Thus, also pop the wallet from your *baggage*.
+
+Now you’re good to go. Bon voyage!
+
+---