immutable-util-functions.js

const getImmutableTodosByCategory = (todos, categoryId) => (
  todos.filter(todo => (
    todo.get('categories').filter(category => category.get('id') === categoryId).size > 0
  )
)
               
const getTodosByCategory = (todos, categoryId) => (
  todos.filter(todo => (
    todo.categories.filter(category => category.id === categoryId).length > 0
  )
)