How to iterate over an array of objects Ruby

Question

I created a class and added objects like so:

class Tops
  def initialize(neckline, brand, maincolour, style)
    @neckline = neckline
    @brand = brand
    @maincolour = maincolour
    @style = style
  end
end

top1 = Tops.new("Sweetheart", "Miss Selfridge", "Blue", "Bardot")
top2 = Tops.new("Scoop", "Target", "Pink", "Vest")
top3 = Tops.new("Boat", "Unknown", "Red", "Tank")

I then used the push method to add some of these objects into an empty array.

currentTopChoices = []
currentTopChoices.push(top1,top3)

I then used some the each method to run a block of code or each object in this array

currentTopChoices.each { |x| puts @neckline }

So my aim was really to get an output of each neckline of the objects in the array but I get an output of:

Boat
Boat

When I really wanted:

Sweetheart
Boat

Which is really the neckline of the last object but printed twice. I get no error messages so what exactly am I missing here?

just make a setter or add a attr_accessor then use map for the new array. — Motombo
– Motombo, Commented Sep 2, 2016 at 21:12
I cannot reproduce this. Since @neckline is un-initialized, it should evaluate to nil and thus print two empty lines, not Boat. — Jörg W Mittag
– Jörg W Mittag, Commented Sep 3, 2016 at 8:23

pdoherty926 · Accepted Answer · 2016-09-02 22:31:18Z

1

If you don't mind adding an attr_accessor to Tops (which will provide a Top#neckline accessor method), you can use Array#map or (its alias Array#collect) to build a collection of necklines:

class Tops
  attr_accessor :neckline

  def initialize(neckline, brand, maincolour, style)
    @neckline = neckline
    @brand = brand
    @maincolour = maincolour
    @style = style
  end
end

top1 = Tops.new("Sweetheart", "Miss Selfridge", "Blue", "Bardot")
top2 = Tops.new("Scoop", "Target", "Pink", "Vest")
top3 = Tops.new("Boat", "Unknown", "Red", "Tank")

[top1, top3].map(&:neckline) # => ["Sweetheart", "Boat"]
# or, more explicitly
[top1, top3].map { |top| top.neckline } # => ["Sweetheart", "Boat"]

edited Sep 2, 2016 at 22:31

answered Sep 2, 2016 at 21:11

pdoherty926

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Comments

nPn · Accepted Answer · 2016-09-03 02:43:48Z

The problem is that somehow you are confusing yourself by either not showing all your code, or maybe running this in irb, where at some point you had a statement like?

@neckline = "Boat"

For example the code you posted, if placed directly in a file_name.rb like so:

class Tops
  def initialize(neckline, brand, maincolour, style)
    @neckline = neckline
    @brand = brand
    @maincolour = maincolour
    @style = style
  end
end

top1 = Tops.new("Sweetheart", "Miss Selfridge", "Blue", "Bardot")
top2 = Tops.new("Scoop", "Target", "Pink", "Vest")
top3 = Tops.new("Boat", "Unknown", "Red", "Tank")

currentTopChoices = []
currentTopChoices.push(top1,top3)

currentTopChoices.each { |x| puts @neckline }

and then run using ruby file_name.rb

would just produce 2 blank lines because @neckline is not define at this scope (toplevel), so it's value is nil

To get this to work the way you intend you can add

attr_reader :neckline

and then refer to x.neckline within the block you pass to each, since x will take one the value of each of the Tops objects in currentTopChoices

note: attr_accessor adds both a setter and a getter for neckline, if you only need read access to that property than that's all you should allow (which is what you get with attr_reader ), if you really need to both get and set the value of neckline on an instance after creating it then att_accessor would make sense.

Here is an updated version of your code that should behave as you are expecting.

class Tops
  attr_reader :neckline  # added to allow read access to @neckline
  def initialize(neckline, brand, maincolour, style)
    @neckline = neckline
    @brand = brand
    @maincolour = maincolour
    @style = style
  end
end

top1 = Tops.new("Sweetheart", "Miss Selfridge", "Blue", "Bardot")
top2 = Tops.new("Scoop", "Target", "Pink", "Vest")
top3 = Tops.new("Boat", "Unknown", "Red", "Tank")

currentTopChoices = []
currentTopChoices.push(top1,top3)

currentTopChoices.each { |x| puts x.neckline }  # access the neckline property for each element

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