ordered_list

v0.1.0

OrderedList

Provides a set of algorithms for sorting and reordering the position number of maps in a list. All of the functions expect a List where each element is a Map with a :postion key.

iex> original_list = [%{id: 1, position: 1},%{id: 2, position: 2}, %{id: 3, position: 3},%{id: 4, position: 4},%{id: 5, position: 5}] 
iex> OrderedList.insert_at(original_list,%{id: 4, position: 4}, 2)
{  
  #Unchanged
  [%{id: 1, position: 1}, %{id: 5, position: 5}],
  #Changed
  [
    {%{id: 2, position: 2}, %{ position: 3 }}, 
    {%{id: 3, position: 3}, %{ position: 4 }}, 
    {%{id: 4, position: 4}, %{ position: 2 }}
  ]
}

The return value is a Tuple where the first element is a list of maps that haven’t had their position changed. The second element is a List of tuples where the first element is the original Map and the second is params for the new position. The idea being that you would be able to pass each Map in the second list to create changesets with Ecto.

post = MyRepo.get!(Post, 42)
posts = MyRepo.all(Post)
{ same_positions, new_positions } = OrderedList.insert_at(posts, post, 3)

changesets =  Enum.map new_positions, fn ({orginal, params}) ->
  Post.changeset(orginal, params)
end

Repo.transaction fn ->
  Enum.each changesets, fn (post) ->
    case MyRepo.update post do
      {:ok, model}        -> # Updated with success
      {:error, changeset} -> # Something went wrong
    end
  end
end

Summary

Functions

first?(list, original_element)

Returns a boolean value if the element is in the first :position in the list

insert_at(list, original_element, new_position)

Retuns a Tuple of two elements, the first being a List of maps that don’t need there position updated. The second is a List of tuples with the first element being the original Map and second being a Map with new :position

last?(list, original_element)

Returns a boolean value if the element is in the last :position in the list

move_higher(list, original_element)

Moves the original_element one position up the list. Higher up the list means that the position number will be lower

move_lower(list, original_element)

Moves the element one position down the list. Lower down the list means that the position number will be higher

move_to_bottom(list, original_element)

Moves the original_element to the bottom of the list

move_to_top(list, original_element)

Moves the original_element to the top of the list

remove_from_list(list, original_element)

Returns a Tuple that contain two elements, the first being the item to be removed and the second a Tuple containing the changes to positions that have been effected by the removal of the element

Functions

first?(list, original_element)

Returns a boolean value if the element is in the first :position in the list.

  • list - A List where each element is a Map or Struct that contains a :position key.

  • original_element - A Map or Struct that is contained within the list in the first argument

Example:

iex> original_list = [%{id: 1, position: 1},%{id: 2, position: 2}, %{id: 3, position: 3},%{id: 4, position: 4},%{id: 5, position: 5}]
iex> OrderedList.first?(original_list, %{id: 1, position: 1})
true
iex> OrderedList.first?(original_list, %{id: 2, position: 2})
false
insert_at(list, original_element, new_position)

Retuns a Tuple of two elements, the first being a List of maps that don’t need there position updated. The second is a List of tuples with the first element being the original Map and second being a Map with new :position.

  • list - A List where each element is a Map or Struct that contains a :position key.

  • original_element - A Map or Struct that is contained within the list in the first argument

  • new_position - An Integer of position that the original_element is moving to.

Example:

iex> original_list = [%{id: 1, position: 1},%{id: 2, position: 2}, %{id: 3, position: 3},%{id: 4, position: 4},%{id: 5, position: 5}] 
iex> OrderedList.insert_at(original_list,%{id: 4, position: 4}, 2)
{  
  #Unchanged
  [%{id: 1, position: 1}, %{id: 5, position: 5}],
  #Changed
  [
    {%{id: 2, position: 2}, %{ position: 3 }}, 
    {%{id: 3, position: 3}, %{ position: 4 }}, 
    {%{id: 4, position: 4}, %{ position: 2 }}
  ]
}
last?(list, original_element)

Returns a boolean value if the element is in the last :position in the list.

  • list - A List where each element is a Map or Struct that contains a :position key.

  • original_element - A Map or Struct that is contained within the list in the first argument

Example:

iex> original_list = [%{id: 1, position: 1},%{id: 2, position: 2}, %{id: 3, position: 3},%{id: 4, position: 4},%{id: 5, position: 5}]
iex> OrderedList.last?(original_list, %{id: 5, position: 5})
true
iex> OrderedList.last?(original_list, %{id: 4, position: 4})
false
move_higher(list, original_element)

Moves the original_element one position up the list. Higher up the list means that the position number will be lower.

  • list - A List where each element is a Map or Struct that contains a :position key.

  • original_element - A Map or Struct that is contained within the list in the first argument

Example:

iex> original_list = [%{id: 1, position: 1},%{id: 2, position: 2}, %{id: 3, position: 3},%{id: 4, position: 4},%{id: 5, position: 5}]
iex> OrderedList.move_higher(original_list, %{id: 5, position: 5})
{
  #Unchanged
  [%{id: 1, position: 1}, %{id: 2, position: 2}, %{id: 3, position: 3}], 
  #Changed
  [{%{id: 4, position: 4}, %{position: 5}}, {%{id: 5, position: 5}, %{position: 4}}]
}

The position number will remain unchanged if it is already in the highest position.

move_lower(list, original_element)

Moves the element one position down the list. Lower down the list means that the position number will be higher.

  • list - A List where each element is a Map or Struct that contains a :position key.

  • original_element - A Map or Struct that is contained within the list in the first argument

Example:

iex> original_list = [%{id: 1, position: 1},%{id: 2, position: 2}, %{id: 3, position: 3},%{id: 4, position: 4},%{id: 5, position: 5}]
iex> OrderedList.move_lower(original_list, %{id: 1, position: 1})
{
  #Unchanged
  [%{id: 3, position: 3}, %{id: 4, position: 4}, %{id: 5, position: 5}],
  #Changed 
  [
    {%{id: 1, position: 1}, %{position: 2}}, 
    {%{id: 2, position: 2}, %{position: 1}}
  ]
}

The position number will remain unchanged if it is already in the lowest position.

move_to_bottom(list, original_element)

Moves the original_element to the bottom of the list.

  • list - A List where each element is a Map or Struct that contains a :position key.

  • original_element - A Map or Struct that is contained within the list in the first argument

Example:

iex> original_list = [%{id: 1, position: 1},%{id: 2, position: 2}, %{id: 3, position: 3},%{id: 4, position: 4},%{id: 5, position: 5}]
iex> OrderedList.move_to_bottom(original_list, %{id: 1, position: 1})
{
  #Unchanged
  [],
  #Changed    
  [
    {%{id: 1, position: 1}, %{position: 5}}, 
    {%{id: 2, position: 2}, %{position: 1}}, 
    {%{id: 3, position: 3}, %{position: 2}}, 
    {%{id: 4, position: 4}, %{position: 3}},
    {%{id: 5, position: 5}, %{position: 4}}
  ]
}

The position number will remain unchanged if it is already in the lowest position.

move_to_top(list, original_element)

Moves the original_element to the top of the list.

  • list - A List where each element is a Map or Struct that contains a :position key.

  • original_element - A Map or Struct that is contained within the list in the first argument

Example: 

iex> original_list = [%{id: 1, position: 1},%{id: 2, position: 2}, %{id: 3, position: 3},%{id: 4, position: 4},%{id: 5, position: 5}]
iex> OrderedList.move_to_top(original_list, %{id: 5, position: 5})
{
  #Unchanged
  [],
  #Changed    
  [
    {%{id: 1, position: 1}, %{position: 2}}, 
    {%{id: 2, position: 2}, %{position: 3}}, 
    {%{id: 3, position: 3}, %{position: 4}}, 
    {%{id: 4, position: 4}, %{position: 5}},
    {%{id: 5, position: 5}, %{position: 1}}
  ]
}

The position number will remain unchanged if it is already in the highest position.

remove_from_list(list, original_element)

Returns a Tuple that contain two elements, the first being the item to be removed and the second a Tuple containing the changes to positions that have been effected by the removal of the element.

  • list - A List where each element is a Map or Struct that contains a :position key.

  • original_element - A Map or Struct that is contained within the list in the first argument

Example:

iex> original_list = [%{id: 1, position: 1},%{id: 2, position: 2}, %{id: 3, position: 3},%{id: 4, position: 4},%{id: 5, position: 5}]
iex> OrderedList.remove_from_list(original_list, %{id: 3, position: 3})
{
  #Remove
  %{id: 3, position: 3},
  {
    #Unchanged
    [%{id: 1, position: 1}, %{id: 2, position: 2}],
    #Changed    
    [   
      {%{id: 4, position: 4}, %{position: 3}},
      {%{id: 5, position: 5}, %{position: 4}}
    ]
  }
}