[ruby-on-rails] Rounding float in Ruby

I'm having problems rounding. I have a float, which I want to round to the hundredth of a decimal. However, I can only use .round which basically turns it into an int, meaning 2.34.round # => 2. Is there a simple effect way to do something like 2.3465 # => 2.35

You can add a method in Float Class, I learnt this from stackoverflow:

class Float
    def precision(p)
        # Make sure the precision level is actually an integer and > 0
        raise ArgumentError, "#{p} is an invalid precision level. Valid ranges are integers > 0." unless p.class == Fixnum or p < 0
        # Special case for 0 precision so it returns a Fixnum and thus doesn't have a trailing .0
        return self.round if p == 0
        # Standard case  
        return (self * 10**p).round.to_f / 10**p
    end
end

def rounding(float,precision)
    return ((float * 10**precision).round.to_f) / (10**precision)
end

If you just need to display it, I would use the number_with_precision helper. If you need it somewhere else I would use, as Steve Weet pointed, the round method

For ruby 1.8.7 you could add the following to your code:

class Float
    alias oldround:round
    def round(precision = nil)
        if precision.nil?
            return self
        else
            return ((self * 10**precision).oldround.to_f) / (10**precision)
        end 
    end 
end

you can use this for rounding to a precison..

//to_f is for float

salary= 2921.9121
puts salary.to_f.round(2) // to 2 decimal place                   

puts salary.to_f.round() // to 3 decimal place          

Pass an argument to round containing the number of decimal places to round to

>> 2.3465.round
=> 2
>> 2.3465.round(2)
=> 2.35
>> 2.3465.round(3)
=> 2.347

You can also provide a negative number as an argument to the round method to round to the nearest multiple of 10, 100 and so on.

# Round to the nearest multiple of 10. 
12.3453.round(-1)       # Output: 10

# Round to the nearest multiple of 100. 
124.3453.round(-2)      # Output: 100

what about (2.3465*100).round()/100.0?