Why Does 'Puts(Nil or 4)' Fail in Ruby

no implicit conversion of nil into String error

One of (or more) values in string

finalStatsFile.puts col_date+", "+col_constant1+", "+ col_appYear+", "+col_statsDesc+", "+col_constant2+", "+col_keyStats+", "+col_weeklyTotal

became nil. To fix the output you should explicitly cast them to strings:

finalStatsFile.puts col_date.to_s + ", " + 
                    col_constant1.to_s + ", " + 
                    col_appYear.to_s + ", " + 
                    col_statsDesc.to_s + ", " +
                    col_constant2.to_s + ", " +
                    col_keyStats.to_s + ", " + 
                    col_weeklyTotal.to_s 

BTW, the whole clause might be rewritten in more rubyish manner:

finalStatsFile.puts [ col_date,
                      col_constant1,
                      col_appYear,
                      col_statsDesc,
                      col_constant2,
                      col_keyStats,
                      col_weeklyTotal ].map(&:to_s).join(', ')

Ruby: undefined method `[]' for nil:NilClass when trying to get Enumerator on an Array of Hashes

undefined method `[]' for nil:NilClass says you tried to do something[index] but something is nil. Ruby won't let you use nil as an array (ie. call the [] method on it).

The problem is not on the attributs.each line but on the line following which calls the [] method on attribut.

typeAttribut = attribut['objectTypeAttribute']

This indicates something in attributs is nil. This could happen if attributsParam is a list that contains nil like so.

attributsParam = [nil];
attributs = Array(attributsParam);

# [nil]
puts attributs.inspect

Simplest way to debug it is to add puts attributs.inspect just before the loop.

Also consider if you really need the attributs = Array(attributsParam) line or if it's already something Enumerable.

in `_main': undefined method `run' for nil:NilClass (NoMethodError)

At the point where you call request.run the value for request is nil. This is why you are seeing the error you're given.

This is happening because the line right above it assigns the nil value to the request variable.

You are clearly coming from another language that is not Ruby (some type of C maybe?), by how you've formatted things. It would help for you to get more familiar with Ruby and its idioms. However, best I can tell, you want to do something like this instead:

def _main
   request = MySqliteRequest.new
   request.from('nba_player_data.csv')
   request.select('name')
   request.where('birth_state', 'Indiana')
   request.run
end
_main()

This assumes you've also defined (and in some cases probably overridden) these methods on your MySqliteRequest Object or Model:

from

select

where

However, please note that the way you're going about this is just completely against how Ruby and Ruby on Rails is designed to work.

Ruby Error: nil can't be coerced to Integer

Silvio Mayolo doesn't explain error

Problem with changing instance variable -- is just one of the problem. But reason is another

For example this code:

class Foo
  attr_accessor :bar

  def initialize
    @bar = 0
  end

  def baz
    p x

    10.times do
      if bar < 6
        @bar += 1
      end
    end
  end
end

Foo.new.baz

will raise

undefined local variable or method `x'

but this code:

class Foo
  attr_accessor :bar

  def initialize
    @bar = 0
  end

  def baz
    10.times do
      if bar < 6
        x = 1
        @bar += 1
      else
        p x
      end
    end
  end
end

Foo.new.baz

will print

nil
nil
nil
nil

So factors_list[-1] - idx < 0 in your code raises error. Local variable idx is is declared, but not initialized, because those if branch is not executed

I am very surprised why your question is downvoted. The feeling that readers have not figured out the question, as well as Silvio Mayolo

What does the 'undefined method `+' for nil:NilClass (NoMethodError)' error in my ruby code mean?

The function only works 'a'..'z' as @Jeremty mentioned, so W and ! will be nil.If you want to keep every none alphabet char, the following code maybe help.

def caesar_cipher(string, num)
  alphabet = [*'a'..'z', *'A'..'Z']
  caesar = ""
  string.each_char do |letter|
    old_idx = alphabet.find_index(letter)
    if old_idx.nil?
      caesar += letter
    else
      new_idx = (old_idx + num) % alphabet.count
      caesar += alphabet[new_idx]
    end
  end

  caesar
end

puts caesar_cipher("What a string!",5)  

Why does defined input variable return nil after exception occurs?

I'm not sure this is what you want but I try

input = gets.chomp
begin
  number = Integer(input)
  puts "your number plus five: #{number + 5}"
rescue ArgumentError
  puts "#{input} is not a valid number"
end

Comparison of fixnum with nil failed, value not nil

when it runs it gives an error that Fixnum can not be compared with nil and I have no idea why

It's because of this expression:

until (arr[idx] < arr[i]) || (i == arr.length)

Ruby evaluates it from left to right, i.e.:

arr = [2, 8, 4, 3]
idx = 2
i   = 4

until (arr[idx] < arr[i]) || (i == arr.length)
#      arr[ 2 ] < arr[4]
#             4 < nil
#          ArgumentError  

You can fix it by exchanging both checks:

until (i == arr.length) || (arr[idx] < arr[i])
#      4 == 4
#       true

Ruby doesn't evaluate the right hand side because of short-circuit evaluation.

---

You're not asking for a different approach, but I couldn't resist to find a more compact solution. Here's my attempt:

We have to compare the value at the starting index n with its adjacent values, i.e.

• compare array[n] to array[n - 1]
• compare array[n] to array[n + 1]
• compare array[n] to array[n - 2]
• compare array[n] to array[n + 2]
• ...

I would start by writing a method that returns the array of adjacent indices in alternating order, starting at n, i.e. [n - 1, n + 1, n - 2, n + 2, ...]:

def adjacent_indices(size, n)
  (1...size).flat_map { |i| [n - i, n + i] }.reject { |i| i < 0 || i >= size }
end

flat_map returns the aforementioned array. reject is a bounds check, it removes all indices that are below 0 or above the array's size.

Example:

adjacent_indices(5, 0) #=> [1, 2, 3, 4]
adjacent_indices(5, 1) #=> [0, 2, 3, 4]
adjacent_indices(5, 2) #=> [1, 3, 0, 4]
adjacent_indices(5, 3) #=> [2, 4, 1, 0]
adjacent_indices(5, 4) #=> [3, 2, 1, 0]

That looks good.

Using Enumerable#find, we can easily find the first index i whose array value (i.e. array[i]) is larger than the value at index n (i.e. array[n]):

def nearest_larger(array, n)
  adjacent_indices(array.size, n).find { |i| array[i] > array[n] }
end

Example:

#    0  1  2  3
a = [2, 8, 4, 3]
nearest_larger(a, 0) #=> 1
nearest_larger(a, 1) #=> nil
nearest_larger(a, 2) #=> 1
nearest_larger(a, 3) #=> 2

Rails 4: model.where.not does not return nil records

You were on the right track with the last query.

Book.where(category_id: 10).where("author != ? OR author IS NULL", "John Doe")

This should do what you are asking.

Side note, in Rails 5, you can use or with ActiveRecord queries, so you could so something like:

Book.where(category_id: 10).where.not(author: 'John Doe').or(where(author: nil))

Though I'd argue, in this case, the first query is clearer.

Comparison of Integer with nil failed (ArgumentError) while solving Insertion Sort with Ruby

Thanks for the clarification in the comments. I see the problem now.

In the swap algorithm here

elsif list[i] > list[i+1] && i > 0
  len = (list[0..(i+1)].length)
  list2 = list[0..(i+1)]
  list = list - list2
  count = 0
  while count <= len+1
    ...

you are trying to split the array in two. You get list2 which is the first half of the array and then try and get the second half by subtracting list2 from list.

The problem with using subtract here is that if you have duplicates it will remove them and make your lists too short.

In the example [3790,1,780,55,23,50,1111,60,50] you should have a 50 in the first array and a 50 in the second half.

But using subtract removes one of those 50.

When you add the two temporary lists back together you are now one element short (the missing 50) and you get an out of bounds error when you get to the end of the array and try and access this 9th element which no longer exists.

Instead of using subtract here simply use the same method you used to make list2.

list2 = list[0..(i+1)] # All elements in list from position 0 to i+1
list = list[(i+2)..-1] # All elements in list from position i+2 to end of list

Now list and list2 are just the original list split, and when you add them back together are the end they should be the same length

def insertion_sort(list)
  num = list.length
  for i in (0..(num-2))
    if list[i] > list[i+1] && i == 0
      list[i], list[i+1] = list[i+1], list[i]
      i+=1
    elsif list[i] == list[i+1]
      i+=1
    elsif list[i] > list[i+1] && i > 0
      len = (list[0..(i+1)].length)
      list2 = list[0..(i+1)]
      list = list[(i+2)..-1]
      count = 0
      while count <= len+1
        if list2[len-1] < list2[len-2]
           list2[len-2],list2[len-1]= list2[len-1],list2[len-2] 
        elsif  list2[len-1] == list2[len-2]
          count+=1
          len-=len
        else
         count+=1
         len-=1 
        end
      end
       list = list2 + list  
    end
  end
   list
end

p insertion_sort([2,1,4,8,7,3,100,99,8])
p insertion_sort([2,1,4,8,8,7,3,100,99])
p insertion_sort([3790,780,780,1,55])

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