ruby array input

Question

I am trying to write a small function with ruby that gets fed a array from the user and then sums up the data in the array. I have written it as

    def sum(a)
      total = 0
      a.collect { |a| a.to_i + total }
    end

The function then runs through a rspec, which tests it by initially feeding into it a blank array. This this causes the following error

    sum computes the sum of an empty array
    Failure/Error: sum([]).should == 0
    expected: 0
        got: [] (using ==)

So its telling me that when it feeds the blank array in, its supposed to get 0 but instead its getting the array. I tried putting in a if statement written as

    def sum(a)
      total = 0
      a.collect { |a| a.to_i + total }
      if total = [] then { total = 0 end }
    end

but it gives me an error saying

    syntax error, unexpected '}', expecting => (SyntaxError)

what am I doing wrong?

Duplicate of stackoverflow.com/questions/1538789/…

Aaron Kurtzhals
– Aaron Kurtzhals

2013-04-04 17:31:25 +00:00
Commented Apr 4, 2013 at 17:31 — Aaron Kurtzhals
– Aaron Kurtzhals, Commented Apr 4, 2013 at 17:31

Sergio Tulentsev · Accepted Answer · 2013-04-04 17:31:35Z

2

You shouldn't use map/collect for this. reduce/inject is the appropriate method

def sum(a)
  a.reduce(:+)
  # or full form
  # a.reduce {|memo, el| memo + el }

  # or, if your elements can be strings
  # a.map(&:to_i).reduce(:+)
end

answered Apr 4, 2013 at 17:31

Sergio Tulentsev

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3 Comments

000 Over a year ago

This fails for arrays like a = ["123","23","345","678"]. I think Mike F is using .to_i specifically.

000 Over a year ago

How does a.map(&:to_i).reduce(:+) perform with memory usage on large arrays? Would it double the memory usage, or is Ruby smart enough to do this smarter?

Sergio Tulentsev Over a year ago

In ruby 2.0 this could be made lazy. In previous versions, yes, it will create a temp array. Your version is more efficient in that sense. But mine is prettier :)

Community · Accepted Answer · 2017-05-23 10:32:11Z

0

See here: How to sum array of numbers in Ruby?

and here: http://www.ruby-doc.org/core-1.9.3/Enumerable.html#method-i-inject

def sum(a)
    array.inject(0) {|sum,x| sum + x.to_i }
end

edited May 23, 2017 at 10:32

CommunityBot

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answered Apr 4, 2013 at 17:31

000

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2 Comments

Mike F Over a year ago

this worked, thank you. Does it work because it is telling the program to add a zero to each location if that location is blank?

000 Over a year ago

It converts every location to an integer. If it's blank, then it converts to zero.

DigitalRoss · Accepted Answer · 2013-04-04 17:54:58Z

0

gets.split.map(&:to_i).inject(:+)

answered Apr 4, 2013 at 17:54

DigitalRoss

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