0 
def binarysearch(a, b,  tofind, stringarray)
  k=(a+b)/2
  if a==b
    return nil
  end
  if (stringarray[k]).include? tofind
    return stringarray[k]
  end
  if (stringarray[k]<=>tofind)==1
    binarysearch(a,k,tofind,stringarray)
  end
  if (stringarray[k]<=>tofind)==-1
    binarysearch(k,b,tofind,stringarray)
  end
  if (stringarray[k]<=>tofind)==0
    return stringarray[k]
  end
end

This is a binary search algorithm. The a and b are the array indices that it is working on, tofind is a string that it is searching for, and stringarray is an array of strings. Unfortunately, every time that I try to run this function I get the following syntax error:

undefined method `include?' for 1:Fixnum (NoMethodError)`

But this is not a fixnum. I am pretty new to Ruby, so I could easily be missing something obvious. Any advice?

This is where I declare stringarray: (Netbeans says that it is an array)

  strings=Array.new
  newstring=""
  until newstring=="no" do
    newstring=gets.chomp
    strings[strings.size]=newstring
  end
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5
  • 6
    Just a note: Ruby is not C. While the above is a valid program, it is obtuse and convoluted. Half of learning Ruby is learning to write well-thought code that is expressive. Had you done that here, I suspect you wouldn't be running into this problem. Check out Eloquent Ruby by Russ Olson for more. Commented Mar 3, 2011 at 21:01
  • I have rewritten the above code in a Rubyier way: voidptr.heroku.com/pastes/…. Still doesn't work though, but it gives you an idea of how Ruby code usually looks. Have fun! Commented Mar 3, 2011 at 21:07
  • 2
    Please provide a sample array and invocation showing this problem. Clearly stringarray[k] is a Fixnum. Commented Mar 3, 2011 at 21:19
  • Added some code showing where I declare stringarray (with a different name) Commented Mar 3, 2011 at 21:59
  • @coreyward: your code is very pretty :) I'm fixing the rest of the program now Commented Mar 3, 2011 at 22:03

2 Answers 2

Reset to default
5

This adds binary search to all arrays:

class Array
  def binarysearch(tf,lower=0,upper=length-1)
    return if lower > upper
    mid = (lower+upper)/2
    tf < self[mid] ? upper = mid-1 : lower = mid+1
    tf == self[mid] ? mid : binarysearch(tf,lower,upper)
  end
end

Then you can use it like this:

(0..100).to_a.binarysearch(25)
=> 25
(0..100).to_a.binarysearch(-1)
=> nil

Or specify your lower and upper bound from the beginning:

(0..100).to_a.binarysearch(25, 50, 100)
=> nil
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Comments

0

The stringarray that is passed to your function is not actually an array of strings, but just a simple string. Using the [] method on a string returns the character code of the character at the given position, as a Fixnum; so stringarray[k] returns the character code of the character at position k in the string. And as the error says, Fixnum does not have an include?.

Even if stringarray was an array of strings, I'm not sure why you would do string comparisons with include?. include? is for finding out if items exist in an array. To compare strings, just use ==.

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8 Comments

Note that using the [] method on a string returns the character at that index as of Ruby 1.9 (no longer the character code as in 1.8).
[] is a method, not an operator.
Yeah yeah, I'm using the term loosely. Even the pickaxe book refers to them as operators as well as methods. I'll fix it though.
.include on a string tests if the given substring exists in that string
Well, nothing is certain, of course, but it does seem reasonable that somewhere in your code on its way to the binarysearch method there is an error that turns the array of strings into a simple string. You could check this by a debug printout of stringarray.class at the beginning of binarysearch.
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