Error regarding using a block within a block in Ruby - Array can't be coerced into Fixnum (TypeError)

Question

This is in regards to project Euler problem #1. When I run this code line by line in irb, I get the expected answer, but when I run it from a .rb file, it throws error "Array can't be coerced into Fixnum (TypeError)"

Code:

# defines the list of integers from 'n' downto 0
def Zi (a, b) 
   (a.downto b).lazy
end

# the equation numberOfOccurances(smallestMultiple + largestMultiple)/2 gives the sum of all the multiples for a given range
# so, below, multipleCounts[i](multiples[i] + lastMultiples[i])/2 => multipleCounts[i](lastAndFirstMultipleSums[i])/2
# gives the arbitrary sum of multiples of a give number in multiples for the specified range.
def find_sum_for_each_multiple(from, to, *multiples)
   myReverseArr = Zi to, from
   lastMultiples = multiples.map { |m| myReverseArr.find { |i| i % m == 0 } }
   multipleCounts = lastMultiples.zip(multiples).map { |ms| ms.reduce(:/) }
   lastAndFirstMultipleSums = lastMultiples.zip(multiples).map { |ms| ms.reduce(:+) }
   sumsOfEachMultiple = lastAndFirstMultipleSums.zip(multipleCounts).map { |xs| xs.reduce(:*) }.map { |x| x/2 }
end

def find_sum_of_multiples(from, to, *multiples)
   sumsOfEachMultiple = find_sum_for_each_multiple(from, to, multiples)

   commonMultiples = []
   (0..(multiples.length - 1)).each do |i|
      ((i+1)..(multiples.length - 1)).each do |j|
         commonMultiples << (multiples[i] * multiples[j])
      end
   end

   sumsOfCommonMultiples = find_sum_for_each_multiple(from, to, commonMultiples)

   totalSum = (sumsOfEachMultiple.inject { |sum, x| sum + x }) - (sumsOfCommonMultiples.inject { |sum, x| sum + x })
end

puts find_sum_of_multiples(0, 999, 3, 5)

Error message:

C:\Users\[User]>ruby euler1.rb
euler1.rb:11:in `%': Array can't be coerced into Fixnum (TypeError)
        from euler1.rb:11:in `block (2 levels) in find_sum_for_each_multiple'
        from euler1.rb:11:in `downto'
        from euler1.rb:11:in `each'
        from euler1.rb:11:in `each'
        from euler1.rb:11:in `find'
        from euler1.rb:11:in `block in find_sum_for_each_multiple'
        from euler1.rb:11:in `map'
        from euler1.rb:11:in `find_sum_for_each_multiple'
        from euler1.rb:18:in `find_sum_of_multiples'
        from euler1.rb:32:in `<main>'

I'm running on a core i7 Windows 7 64bit machine with Ruby version 2.0.0p0 (2013-02-24) [x64-mingw32]

whoever down-voted me, mind explaining why I was down-voted? This seems like a legitimate question to me... If I can execute the same code line by line in the interpreter and get no errors, but I get an error when running the code from a script, this would imply at least to me that my logic is correct, but there is something specific about the language implementation that I am missing. I did Google around a little, but I didn't find much that I thought pertained to this error. Could it be a defect in the interpreter? — josiah
– josiah, Commented Aug 12, 2013 at 6:57

Santhosh · Accepted Answer · 2013-08-12 07:26:10Z

1

commonMultiples is already an Array, and in find_sum_for_each_multiple, it gets converted to an Array of Arrays

Change this line

sumsOfCommonMultiples = find_sum_for_each_multiple(from, to, commonMultiples)

to

sumsOfCommonMultiples = find_sum_for_each_multiple(from, to, *commonMultiples)

answered Aug 12, 2013 at 7:26

Santhosh

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3 Comments

josiah Over a year ago

Aaah! So it was just a bit of Ruby syntax I was missing. Thanks! This worked for me!

josiah Over a year ago

I also want to add that I know this isn't a full solution yet - if you try this method with 3 or more multiples it will break because the sums of common multiples calculation doesn't yet find all of the common multiple duplications. To do so, I believe I would have to edit the code to calculate not only the sums of the common multiples of all pairs (2s), but also of triplets (3s), etc. on up to n where n is the number of multiples. Still sort of thinking this one out.

Santhosh Over a year ago

I didnt try to understand the logic behind this code. Anyways good luck with the problem. :)

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