Using array#select with a helper method doesn't work?

Question

The no_repeats method is to check if any of the years in the range have repeating number. I paired it with a no_repeat? method that checks individual years.

def no_repeats(year_start, year_end)
  no_repeat_years = [year_start..year_end].select { |year| no_repeat?(year) }
end

def no_repeat?(year)
  numbers = year.split("")
  numbers.each do |n|
    if numbers.count(n) > 1
      return false
    end
  end

  return true
end

When I try to run the no_repeats, I'm getting the following error:

undefined method `split' for 1980..2000:Range (NoMethodError)

Why is the entire range getting plugged into the helper function?

Jeremy Rodi · Accepted Answer · 2015-07-27 21:06:19Z

2

On the third line, you have [year_start..year_end]. This is not what you want. What this does is it creates an array containing 1 element: your range. So this becomes equivalent to this:

years = year_start..year_end
value = [years]
value.select do |year|
  year.class # => Range
end

So, instead of [year_start..year_end], you should do (year_start..year_end). Instead of creating an array, this puts precedence on the range, so it will still work as expected (i.e. the #select method will be called on the range instead of year_end).

answered Jul 27, 2015 at 21:06

Jeremy Rodi

2,5052 gold badges22 silver badges42 bronze badges

Sign up to request clarification or add additional context in comments.

6 Comments

Steals Over a year ago

Thank you! That makes sense now.

Jeremy Rodi Over a year ago

No problem! Don't forget to accept the answer if you're content with it.

Steals Over a year ago

Just a last question, does that mean that [0..5] is a range but (0..5) would create an array of the range numbers?

Jeremy Rodi Over a year ago

No. [] creates an array, () does nothing. [1, 2, 3] would create an array containing three elements, whereas (1, 2, 3) would error. () is used to manually specify precedence; for example, when doing math, 1 + 2 * 3 would result in 7, but (1 + 2) * 3 would result in 9.

Steals Over a year ago

Ok, thank you. I hope this doesn't sound dumb, but I'm trying to understand why: [1, 2, 3].select {|n| n.even?} works but [1..3].select {|n| n.even?} doesn't? Doesn't [1..3] technically create an array?

|

Collectives™ on Stack Overflow

Using array#select with a helper method doesn't work?

1 Answer 1

6 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

6 Comments

Your Answer

Sign up or log in

Post as a guest

Related