to_d to always return 2 decimals places in ruby

Question

I'm dealing with currencies and I want to round down the number to 2 decimal places. Even if the number is 500.0, I would like it to be 500.00 to be consistent. When I do "500.00".to_d it converts it to 500.0.

Whats a good way of changing this behavior? I also use this method to round down to 2 digits and make sure it always has 2 decimals.

def self.round_down(x, n=2)
    s = x.to_s      
    l = s.index('.') ? s.index('.') + 1 + n : s.length
    s = s[0, l]
    s =  s.index('.') ? s.length - (s.index('.') + 1) == 1 ? s << '0' : s : s << '.00'      
    s.to_f
end

score 127 · Answer 1 · edited Dec 10 '15 at 02:28

127

In addition to mcfinnigan's answer, you can also use the following to get 2 decimal places

'%.2f' % 500 # "500.00"

This use case is known as the string format operator

edited Dec 10 '15 at 02:28

Todd

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answered Apr 09 '13 at 11:30

jvnill

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Caveat: this will round down or UP, eg. 500.016 becomes 500.02 – webaholik Oct 15 '18 at 01:38
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yep expected behavior would be to follow the rules for rounding numbers – jvnill Oct 15 '18 at 09:48

Stefan · Answer 2 · 2017-12-05T07:12:18.450

68

Since you are using Rails and this seems to be related to a view, there's number_with_precision:

number_with_precision(500, precision: 2)
#=> "500.00"

I18n.locale = :de
number_with_precision(500, precision: 2)
#=> "500,00"

For currencies I'd suggest number_to_currency:

number_to_currency(500)
#=> "$500.00"

edited Dec 05 '17 at 07:12

answered Apr 09 '13 at 11:36

Stefan

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Just want to add that this answer covers a nil value, its great for `.erb` files. – ricks Aug 10 '21 at 13:19
For using the above solution you would want to add this `include ActionView::Helpers::NumberHelper` – Dipansh Khandelwal Feb 16 '23 at 17:54

score 37 · Answer 3 · answered Apr 09 '13 at 11:27

37

Here's a hint. 500.00 is a representation of the number 500.0

Specifically, sprintf will help you:

irb(main):004:0> sprintf "%.2f", 500.0
=> "500.00"

answered Apr 09 '13 at 11:27

mcfinnigan

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As the proverb goes, Real Programmers can write C in *any* language! `'%.2f' % 500` is the Ruby idiom. – Camille Goudeseune Feb 18 '14 at 18:30
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@CamilleGoudeseune I blame it on far too many years of Java :/ – mcfinnigan Feb 19 '14 at 08:37
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sprintf is more explicit than % and I can easily get help about formatting parameters by pressing F1 on sprintf in my IDE – Lev Lukomsky Feb 24 '16 at 16:37
Caveat: this will round down or UP, eg. 500.016 becomes 500.02 – webaholik Oct 15 '18 at 01:38

score 13 · Answer 4 · edited May 23 '17 at 12:34

13

Do not use floating point numbers to represent money. See this question for a good overview of why this is a bad idea.

Instead, store monetary values as integers (representing cents), or have a look at the money gem that provides lots of useful functionality for dealing with such values.

edited May 23 '17 at 12:34

Community

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answered Apr 09 '13 at 11:36

Lars Haugseth

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score 2 · Answer 5 · answered Oct 15 '18 at 01:42

There was a requirement to round DOWN.

Most other answers round 500.016 UP to 500.02

Try:

def self.round_down(x, n = 2)
  "%.#{n}f" % x.to_d.truncate(n)
end

irb(main):024:0> x=500.0; '%.2f' % x.to_d.truncate(2)
=> "500.00"
irb(main):025:0> x=500.016; '%.2f' % x.to_d.truncate(2)
=> "500.01"

to_d to always return 2 decimals places in ruby

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