Ruby: Rounding float in Ruby

Question

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

Solution 1

When displaying, you can use (for example)

>> '%.2f' % 2.3465
=> "2.35"

If you want to store it rounded, you can use

>> (2.3465*100).round / 100.0
=> 2.35

Solution 2

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

Solution 3

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          

Solution 4

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

Solution 5

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

View more solutions

Comments

[Mark Embling]

This would seem more sensible than multiplying, rounding and dividing. +1

[Mindey I.]

Hmm this method doesn't seem to be in ruby 1.8.7. Maybe in 1.9?

[Steve Weet]

@Brian. This is definitely in 1.9 and is also in rails (Which this question was tagged with)

[Noah Sussman]

Thanks. I didn't realize sprintf would take care of rounding for me. sprintf '%.2f', 2.3465 also works.

[bobmagoo]

Ruby 1.8.7's round method doesn't have this ability, adding the decimal place rounding parameter is a 1.9 ability

[TheOneTeam]

value.round(2) is better than this solution

[Excalibur]

Keep in mind that 2.3000.round(2) => 2.3 and sprintf '%.2f', 2.300 => 2.30. In my opinion this is a flaw in round(), or it should have an option to preserve trailing zeros.

[Roobie Nuby]

@Excalibur 2.3000.round(2) is a number, not a string. There is no way that the number 2.3 is different from 2.30, so there is no way to have an option to preserve trailing zeros. You could make your own class of numbers_with_significance but then we already have strings.

[Smar]

Note that number_with_precision is Rails-only method.

[likethesky]

Note that although this does work for two decimal places, there's a flaw in '%.3f' % 1.2345 (3 decimal places, not 2), however!! Same for sprintf as well. Beware. That will return => 1.234 not => 1.235 as most would expect (iow, after the 2nd decimal, sprintf rounds 5 down and only rounds a 6 up). That's why Kit Ho's comment above has 25+ upvotes. Safer to use, '%.3f' % 1.2345.round(3) so the number is properly rounded by .round first, then formatted (with trailing zeros, if need be).

[NotAnAmbiTurner]

Note that you don't get trailing zeros with this, so 1.1.round(2) => 1.1 not 1.10

[NAREN PUSHPARAJU]

Is there any way to avoid rounding of the numbers that doesn't have any decimels in it ? like if it is 0 it should as 0 and not 0.0

[ralphmerridew]

sprintf rounds 0.5 to the nearest even digit. '%.3f' % 1.2355 and '%.3f' % 1.2365 both give "1.236" .round rounds 0.5 up

[Pablo]

2.4.round(3) => 2.4