Vfrdtyky

With the following code:

[

  %Quizz{

    question: "L'unità d' Italia",

    answers: [

      %{answer: 1900, result: false},

      %{answer: 1861, result: true},

      %{answer: 1848, result: false},

    ]

  },

  %Quizz{

    question: "La Rivoluzione Francese",

    answers: [

      %{answer: 1789, result: true},

      %{answer: 1818, result: false},

      %{answer: 1766, result: false},

    ]

  },

  %Quizz{

    question: "La scoperta dell'America",

    answers: [

      %{answer: 1280, result: false},

      %{answer: 1500, result: false},

      %{answer: 1492, result: true},

    ]

  }

]

I would like to shuffle the 3 quizz structs using Enum.shuffle and shuffle the list of answers for each struct. I am able to shuffle the list but I'm struggling to updated the answers list for each struct. How can I do that?

You can shuffle the list and then map over it, replacing each answers field with a shuffled version of it

Enum.shuffle(list_of_quizzes)

|> Enum.map(fn(%{answers: answers} = quizz) -> 

    %{quizz | answers: Enum.shuffle(answers)}

end)

I would go with Kernel.SpecialForms.for/1 comprehension:

for quizz <- Enum.shuffle(quizzes),

  do: %Quizz{quizz | answers: Enum.shuffle(quizz.answers)}

or, other way round:

for quizz <- Enum.shuffle(quizzes),

    answers = Enum.shuffle(quizz.answers),

  do: %Quizz{quizz | answers: answers}

You can also use Map.update!/3 or Kernel.update_in/3:

quiz_list

|> Enum.shuffle

|> Enum.map(fn q -> Map.update!(q, :answers, &Enum.shuffle/1) end)