Ruby array object find

Question

I am trying out ruby by making a program i need. I have a custom class, and I need an array of objects of that class. This custom class has some attributes that change in the course of the program. How can I find a specific object in my array, so I can access it and change it?

class Mathima
  attr_accessor :id, :tmimata

  def initialize(id)
    @id = id
    @tmimata = []
  end
end


# main
mathimata = []

previd = id = ""
File.read("./leit/sortedinput0.txt").lines do |line|
  array = line.split(' ')          # i am reading a sorted file
  id = array.delete_at(0)          # i get the first two words as the id and tmima
  tmima = array.delete_at(0)

  if previd != id
    mathimata.push(Mathima.new(id))  # if it's a new id, add it
  end

  # here is the part I have to go in mathimata array and add something in the tmimata array in an object. 

  previd = id
end

How do you identify which Mathima object you want to add something to? And what is that "something", is it the contents of tmima? — Mark Thomas
– Mark Thomas, Commented Nov 22, 2010 at 13:43
thank you all. I used a hash for mathimata and it's working just fine. — pvinis
– pvinis, Commented Nov 24, 2010 at 7:09

Petrik de Heus · Accepted Answer · 2010-11-22 22:05:54Z

2

Use a Hash for mathimata as Greg pointed out:

mathimata = {}
File.read("./leit/sortedinput0.txt").lines do |line|
  id, tmima, rest = line.split(' ', 3)
  mathimata[id] ||= Mathima.new(id)
end

edited Nov 22, 2010 at 22:05

answered Nov 22, 2010 at 13:54

Petrik de Heus

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1 Comment

the Tin Man Over a year ago

As ids gets longer this will get slower and slower because of the lookup. A Hash would be faster.

mpapis · Accepted Answer · 2010-11-22 13:30:37Z

2

mathima = mathimata.find{|mathima| mathima.check() }
# update your object - mathima

answered Nov 22, 2010 at 13:30

mpapis

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Comments

the Tin Man · Accepted Answer · 2010-11-22 15:35:20Z

Array.find() lets you search sequentially through an array, but that doesn't scale well.

I'd recommend that if you are dealing with a lot of objects or elements, and they're unique, then a Hash will be much better. Hashes allow indexed lookup based on their key.

Because of you are only keeping unique IDs either a Set or a Hash would be a good choice:

mathimata.push(Mathima.new(id))  # if it's a new id, add it

Set is between Array and a Hash. It only allows unique entries in the collection, so it's like an exclusive Array. It doesn't allow lookups/accesses by a key like a Hash.

Also, you can get your first two words in a more Ruby-like way:

array = line.split(' ')          # i am reading a sorted file
id = array.delete_at(0)          # i get the first two words as the id and tmima
tmima = array.delete_at(0)

would normally be written:

id, tmima = line.split(' ')[0, 2]

or:

id, tmima = line.split(' ')[0 .. 1]

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