Ruby - Delete from array of arrays based from Parameter

Question

I'm trying to write a function that will remove an array from a 3d array where an array has a matching String name.

before(:each) do
  @topic1 = Topic.new 4,'topic 1'
  @topic2 = Topic.new 7,'topic 2'
  @topic3 = Topic.new 5,'topic 3'
  @subject = Subject.new 'Module 1',2,5
end

parameters are No_of_Lectures and Name

@topics = [5,'Topic1'], [3,'Topic2'], [5,'Topic3']

Basically I'd like to remove the array where Name = 'Topic1' or return null if it's not in the list.

What I have so far is

def findTopic name
  @topics.find {|topic| topic.name == name }
end


def removeTopic name_in
  if @topics.findTopic(name)
    @topics.delete_if {|key, name| name == name_in } 
    topic
  else
    null
  end
end

What's the specific issue? That's how you delete an item from an array. — Dave Newton
– Dave Newton, Commented Nov 11, 2015 at 22:03
What about everything else? Would this function return the topic removed if it is removed and return null if its not in the list? — ChrisM
– ChrisM, Commented Nov 11, 2015 at 22:18
topic isn't defined in the method, so it wouldn't even run (unless it's a method as well). — Dave Newton
– Dave Newton, Commented Nov 11, 2015 at 22:53
Sorry didnt include that part. So are we good to go with rspec testing now? The function seems like its ok? — ChrisM
– ChrisM, Commented Nov 11, 2015 at 22:59
Probably should have been worrying the test first. But sure-if you're testing correctly you'll know if it's OK-that's kind of the point. — Dave Newton
– Dave Newton, Commented Nov 11, 2015 at 23:48

7stud · Accepted Answer · 2015-11-12 06:58:56Z

3

a 3d array

Your arrays are two dimensional.

return null if its not in the list.

null doesn't exist in ruby--there is nil, though.

def remove(target, array2D)

  results = array2D.reject do |arr|
    arr.last == target
  end

  results.size == array2D.size ? nil : results
end

test_arrays = [
  [[5,'Topic1'], [3,'Topic2'], [5,'Topic3']],
  [[5,'Topic4'], [3,'Topic5'], [5,'Topic6']]
]

test_arrays.each do |array2D|
  p remove('Topic2', array2D)
end

--output:--
[[5, "Topic1"], [5, "Topic3"]]
nil

On the other hand, a solution for this question:

remove a topic from the list. Returns the topic removed; otherwise, return null when topic is not currently in the list.

is:

def remove(target, array2D)

  array2D.each_with_index do |arr, index|
    if arr.last == target
      array2D.delete_at(index)
      return arr
    end
  end

  return nil

end

test_arrays = [
  [[5,'Topic1'], [3,'Topic2'], [5,'Topic3']],
  [[5,'Topic4'], [3,'Topic5'], [5,'Topic6']]
]

test_arrays.each do |array2D|
  p remove('Topic2', array2D)
end

--output:--
[3, "Topic2"]
nil

edited Nov 12, 2015 at 6:58

answered Nov 11, 2015 at 21:59

7stud

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7 Comments

ChrisM Over a year ago

Thanks can you explain what the results = line does?

Dave Newton Over a year ago

While true, this doesn't really address the original issue; using delete should work properly all other things being equal. Whether or not it's a good idea is a separate discussion!

7stud Over a year ago

@ChrisMaher, That assigns the return value of the method to the variable results.

ChrisM Over a year ago

@Dave. Thanks @ 7Stud Strange hearing null doesnt exist. Im following a tutorial and this is the exercise at the end. Heres the instructions. pastebin.com/g49YWGnL

Dave Newton Over a year ago

@ChrisMaher It's sort of the same thing; Ruby's equivalent. One difference is that nil is a class in Ruby, NilClass, which is useful. Is this really a Ruby exercise? If so, it's too bad they didn't follow Ruby naming conventions (snake_case, not camelCase). I'd recommend changing the names to more Ruby-like ones.

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