ruby code with the NoMethodError - ruby

Question

When running the following Ruby code:
#!/usr/bin/env ruby
ar=[]
class String
def to_int
self == self.to_i
end
end
ARGV.each do |a|
ar.push("#{a}")
end
ar.map(&:to_int).sort
ar.each do |x|
print x + " "
end
puts ""
I am getting the following error:
example.rb:14:in `sort': undefined method `<=>' for false:FalseClass (NoMethodError)
This program needs to be running with the command line argument with a list of numbers. Any help will be appreciated.

Answer 1

ARGV.sort.each { |x| print x + " " }
puts

Answer 2

class String
def to_int
self == self.to_i
end
end
This to_int method will return either a true or false. So when you run this line: ar.map(&:to_int).sort, the map method will map the entire array into true or false.
You array will look like [false,false,true,false], which will fail when you run the sort function.
I'm not sure what the purpose of the to_int function is, you just need to map with the simple to_i function, then sort it.
ar.map!(&:to_i).sort
Make sure you use the map! so your original array is modified.
If you do map the array into integers, you will have to modify the print line to
ar.each do |x|
print x.to_s + " "
end
Otherwise you will get an error:
String can't be coerced into Fixnum

Answer 3

When I run this using Ruby 2.3.0, I don't get that error.
I tried Ruby 2.0.0p648 (which comes with OS X), 2.1.5, and 2.2.4, and they don't raise that error either.
It's a bit unclear to me what you're trying to accomplish here.
You're doing things that don't make any sense, but I'll assume you're trying to learn Ruby and you're just trying different things.
#!/usr/bin/env ruby
ar=[]
# This is "monkey patching" String, and is a bad practice.
class String
# A method named "to_int" implies a conversion to integer. But the "to_i" method already does
# that, and this method doesn't convert to an integer, it converts to a boolean.
def to_int
# Comparing the string to itself as an integer. Why would it ever be true?
self == self.to_i
end
end
# I'm assuming that this is intended to convert the argument list to a list of strings.
# But ARGV should already a list of strings.
# And this would be better done as `ar = ARGV.map(&:to_s)`
ARGV.each do |a|
ar.push("#{a}");
end
# This creates an array of values returned by `to_int`, then sorts the array.
# Since `String#to_int` (defined above) returns booleans, it's an array of "false" values, so
# sorting does nothing. But then the value of the `sort` is ignored, since it's not assigned to
# a variable. If you want to modify the order of an existing array, use `sort!`.
# But if you're trying to sort the array `ar` by the numeric values, `ar.sort_by(&:to_i)` would
# do that.
ar.map(&:to_int).sort
ar.each do |x| print x + " "; end
puts ""
It seems like you're trying to print the arguments in their numeric order.
This can be accomplished with
puts ARGV.sort_by(&:to_i).join(" ")