Sort a List of Objects by Using Their Attributes in Ruby

Sort a list of objects by using their attributes in Ruby

The easy solution is

basket.sort_by { |f| [-f.calories, f.name] }

Of course, if this is the canonical sort order for fruit then it should be defined using the <=> method and with the Comparable module mixed into Fruit

Sorting a hash table of objects (by the attributes of the objects) in Ruby

You appear to be confusing sort and sort_by

sort yields two objects from the collection to the block and expects you to return a <=> like value: -1,0 or 1 depending on whether the arguments are equal, ascending or descending, for example

%w(one two three four five).sort {|a,b| a.length <=> b.length}

Sorts the strings by length. This is the form to use if you want to use your <=> operator

sort_by yields one object from the collection at a time and expects you to return what you want to sort by - you shouldn't be doing any comparison here. Ruby then uses <=> on these objecfs to sort your collection. The previous example can e rewritten as

%w(one two three four five).sort_by {|s| s.length}

This is also known as a schwartzian transform

In your case the collection is a hash so things are slightly more complicated: the values that are passed into the block are arrays that contain key/value pairs, so you'll need to extract the person object from that pair. You could also just work on @hash.keys or @hash.values (depending on whether the person objects are keys or values)

Ruby sort by object's attribute based on keyword string

Try use public_send method

array.sort_by { |item| item.public_send(sort_keyword) } 

https://ruby-doc.org/core-2.4.1/Object.html#method-i-public_send

How to sort an array of objects by an attribute of the objects?

I found a method that works from here. I don't understand what the "&" symbol is doing - maybe it's shorthad for "object" since in my case ":lastname" is an attribute of the object that make up the array.

users = users.sort_by &:lastname

note: I don't undertand why but a destructive version won't work. It produces a "undefined method `sort_by!' for #" errror:

users.sort_by! &:lastname

Ruby - sort array of objects by attribute in descending order

You missed to make the age a number

@classroom['students'].sort_by { |st| -st['age'].to_i }

I added a - because you want them in descending order. Otherwise

@classroom['students'].sort_by { |st| st['age'].to_i }.reverse

Sort objects in array by 2 attributes in Ruby with the spaceship operator

Define <=> like this:

   def <=>(other)
     [str.size, str] <=> [other.str.size, other.str]
   end

sorting a ruby array of objects by an attribute that could be nil

How about in Child defining <=> to be based on category.position if category exists, and sorting items without a category as always greater than those with a category?

class Child
  # Not strictly necessary, but will define other comparisons based on <=>
  include Comparable   
  def <=> other
    return 0 if !category && !other.category
    return 1 if !category
    return -1 if !other.category
    category.position <=> other.category.position
  end
end

Then in Parent you can just call children.sort.

Sorting an array of objects by a child's attribute

collection.sort_by do |x|
  x.children.where(:user_id => current_user.id).first.average_score
end

Though I'd look for a pure and faster SQL solution.

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