Checking if a variable is an integer

Question

Does Rails 3 or Ruby have a built-in way to check if a variable is an integer?

For example,

1.is_an_int #=> true
"dadadad@asdasd.net".is_an_int #=> false?

possible duplicate of [Does ruby 1.9.2 have an is_a? function?](http://stackoverflow.com/questions/4282273/does-ruby-1-9-2-have-an-is-a-function) — Andrew Grimm, Jan 04 '11 at 02:09
Rather than caring whether a variable is an integer, you should check to see if the variable responds to `to_i`. That's part of Ruby's "duck typing": If it can act like an integer, treat it like one. — the Tin Man, Jan 04 '11 at 05:34
@the Tin Man: Not entirely. "hello".to_i returns 0 which may not be what you expect. — EinLama, Jan 04 '11 at 07:40
@Andrew Grimm: it is in content, but the question is different. If you didn't know about "is_a?", you wouldn't know to ask if there is a "is_a?". — Groxx, Jan 04 '11 at 21:30
@EinLama, well, to confuse things further, `'0xdeadbeef'.to_i #=> 0` but `'0xdeadbeef'.to_i(16) #=> 3735928559` as does `'deadbeef'.to_i(16) #=> 3735928559` or `'deadbeef'.to_i(16).to_s(16) #=> "deadbeef"`. We're expected to test to make sure we're catching the corner cases but somethings things get slippery. Otherwise we can go old-school and do it asking about types and be more limiting. This is the crux of the arguments surrounding duck-typing. — the Tin Man, Jan 04 '11 at 23:13
@AnApprentice For your information, `kind_of?` is an alias to `is_a?`. — Jacob Relkin, Jan 05 '11 at 01:20
@JacobRelkin `is_a?` is slightly different; it asks if the object of an instance of a specific class; `kind_of?` asks if it is an instance or child of a specific class. `fido.is_a? Dog` is true; `fido.kind_of? Animal` is true, for example. — Tom Harrison, Oct 28 '13 at 19:51

score 311 · Accepted Answer · edited Feb 12 '20 at 08:06

311

You can use the is_a? method

>> 1.is_a? Integer
=> true
>> "dadadad@asdasd.net".is_a? Integer
=> false
>> nil.is_a? Integer
=> false

edited Feb 12 '20 at 08:06

Purplejacket

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answered Jan 04 '11 at 01:41

mportiz08

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Thats very cool. does that work to validate email addresses to? – AnApprentice Jan 04 '11 at 01:42
73

@AnApprentice Since when was validating email addresses part of the question? – Jacob Relkin Jan 04 '11 at 01:56
5

this wont work if the number comes in a string like "11111111" – Ricbermo Feb 11 '14 at 15:00
look below `Integer(obj) rescue false` This will not work for "1" if you want to check if it will convert – mc. Feb 18 '14 at 18:15
4

@Ricbermo "1111111" is a String. A String that happens to be convertible to and Integer. – Sqeaky Apr 28 '14 at 15:32
@AnApprentice you need to use regular expressions: http://www.regular-expressions.info/ – liver Aug 18 '15 at 03:20
It should return false for decimals, integers are by definition whole numbers. – Jordan Jul 13 '18 at 13:51
@zee Of course it will, as 2.3 is not an Integer, it is a Float. See https://www.rubyguides.com/2016/07/numbers-in-ruby/ for understanding numeric types in Ruby and how they are related. – Mecki Apr 13 '19 at 23:00

Alex D · Answer 2 · 2014-10-17T05:54:32.107

54

If you want to know whether an object is an Integer or something which can meaningfully be converted to an Integer (NOT including things like "hello", which to_i will convert to 0):

result = Integer(obj) rescue false

edited Oct 17 '14 at 05:54

answered Aug 07 '13 at 21:54

Alex D

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Maybe I'm just a noob, but this tweak would have helped me. result = Integer(obj) rescue false. – John Curry Oct 16 '14 at 02:58
@JohnCurry, feel free to edit the answer if you can improve it. That's how SO works. – Alex D Oct 16 '14 at 05:55
3

I did, it got rejected. "This edit deviates from the original intent of the post" But regardless, thank you for your answer, it helped me solve my issue! – John Curry Oct 17 '14 at 00:11
8

Integer('08') will fail because of the string being interpreted as octal, Integer('08', 10) works fine. Just in case. – Jong Bor Lee Mar 10 '15 at 18:38
1

Not sure if `Integer(2.5) => 2` is always a meaningful conversion. – mkataja Apr 24 '17 at 12:12

Jacob Relkin · Answer 3 · 2011-01-04T01:45:45.663

32

Use a regular expression on a string:

def is_numeric?(obj) 
   obj.to_s.match(/\A[+-]?\d+?(\.\d+)?\Z/) == nil ? false : true
end

If you want to check if a variable is of certain type, you can simply use kind_of?:

1.kind_of? Integer #true
(1.5).kind_of? Float #true
is_numeric? "545"  #true
is_numeric? "2aa"  #false

edited Jan 04 '11 at 01:45

answered Jan 04 '11 at 01:40

Jacob Relkin

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This it is exactly what i was looking for the is_numeric? – workdreamer Feb 17 '12 at 16:52
I think this is close, but not exactly correct. For instance, it will fail for ".34". The problem, I think, is that in `\d+?` the `?` specifies a non-greedy match, whereas you probably want an optional match. Changing `\d+?` to `\d*` might fix it, but I'd want to run it through a suite of tests to be sure. This also won't match hex or exponential notation, but I'm sure that's fine for certain use cases. – Jeff Apr 24 '12 at 16:04
1

Why not just to use this regexp: `\A\d+\z`? – NARKOZ Oct 03 '12 at 16:12
1

Compare to the `Integer(obj) rescue false` code from @alex-d below; regexp is difficult to read and not clear in its intent. Both work, I came to this question in an attempt to fix a poorly constructed regexp that was not always working :-) – Tom Harrison Oct 28 '13 at 19:47

score 23 · Answer 4 · edited Mar 06 '15 at 17:59

23

If you're uncertain of the type of the variable (it could be a string of number characters), say it was a credit card number passed into the params, so it would originally be a string but you want to make sure it doesn't have any letter characters in it, I would use this method:

    def is_number?(obj)
        obj.to_s == obj.to_i.to_s
    end

    is_number? "123fh" # false
    is_number? "12345" # true

@Benny points out an oversight of this method, keep this in mind:

is_number? "01" # false. oops!

edited Mar 06 '15 at 17:59

Jaime Gómez

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answered Aug 07 '13 at 20:47

bigpotato

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thanks, you save my day. For anyone that need to check if it float or not can change directly to `obj.to_s == obj.to_f.to_s` just like in my case. – ksugiarto Jun 17 '14 at 09:27
Edmund that's clever! – siwalikm Jul 03 '18 at 14:46
Awesome, i prefer this than Integer('123fh') and rescue exception. – zw963 Aug 24 '18 at 18:22

score 5 · Answer 5 · edited Mar 07 '18 at 23:39

5

You can use triple equal.

if Integer === 21 
    puts "21 is Integer"
end

edited Mar 07 '18 at 23:39

Sebastián Palma

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answered May 03 '16 at 01:48

Tsoodol

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score 5 · Answer 6 · answered Jan 04 '11 at 01:41

5

There's var.is_a? Class (in your case: var.is_a? Integer); that might fit the bill. Or there's Integer(var), where it'll throw an exception if it can't parse it.

answered Jan 04 '11 at 01:41

Groxx

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score 3 · Answer 7 · edited Jun 25 '15 at 21:36

3

A more "duck typing" way is to use respond_to? this way "integer-like" or "string-like" classes can also be used

if(s.respond_to?(:match) && s.match(".com")){
  puts "It's a .com"
else
  puts "It's not"
end

edited Jun 25 '15 at 21:36

the Tin Man

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answered Apr 25 '12 at 20:41

vish

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Cyril Duchon-Doris · Answer 8 · 2019-01-23T11:13:41.293

In case you don't need to convert zero values, I find the methods to_i and to_f to be extremely useful since they will convert the string to either a zero value (if not convertible or zero) or the actual Integer or Float value.

"0014.56".to_i # => 14
"0014.56".to_f # => 14.56
"0.0".to_f # => 0.0
"not_an_int".to_f # 0
"not_a_float".to_f # 0.0

"0014.56".to_f ? "I'm a float" : "I'm not a float or the 0.0 float" 
# => I'm a float
"not a float" ? "I'm a float" : "I'm not a float or the 0.0 float" 
# => "I'm not a float or the 0.0 float"

EDIT2 : be careful, the 0 integer value is not falsey it's truthy (!!0 #=> true) (thanks @prettycoder)

EDIT

Ah just found out about the dark cases... seems to only happen if the number is in first position though

"12blah".to_i => 12

@prettycoder thanks for the heads up, I will fix this immediately in the answer — Cyril Duchon-Doris, Jan 23 '19 at 11:11

score 1 · Answer 9 · edited May 23 '17 at 10:31

To capitalize on the answer of Alex D, using refinements:

module CoreExtensions
  module Integerable
    refine String do
      def integer?
        Integer(self)
      rescue ArgumentError
        false
      else
        true
      end
    end
  end
end

Later, in you class:

require 'core_ext/string/integerable'

class MyClass
  using CoreExtensions::Integerable

  def method
    'my_string'.integer?
  end
end

score 0 · Answer 10 · answered Aug 13 '14 at 17:00

I have had a similar issue before trying to determine if something is a string or any sort of number whatsoever. I have tried using a regular expression, but that is not reliable for my use case. Instead, you can check the variable's class to see if it is a descendant of the Numeric class.

if column.class < Numeric
  number_to_currency(column)
else
  column.html_safe
end

In this situation, you could also substitute for any of the Numeric descendants: BigDecimal, Date::Infinity, Integer, Fixnum, Float, Bignum, Rational, Complex

score 0 · Answer 11 · answered Jan 31 '21 at 12:55

Basically, an integer n is a power of three, if there exists an integer x such that n == 3x.

So to verify that you can use this functions

def is_power_of_three(n)
  return false unless n.positive?

  n == 3**(Math.log10(n)/Math.log10(3)).to_f.round(2)
end

score -1 · Answer 12 · answered Feb 27 '18 at 07:22

-1

Probably you are looking for something like this:

Accept "2.0 or 2.0 as an INT but reject 2.1 and "2.1"

num = 2.0

if num.is_a? String num = Float(num) rescue false end

new_num = Integer(num) rescue false

puts num

puts new_num

puts num == new_num

answered Feb 27 '18 at 07:22

Owais Akbani

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Checking if a variable is an integer

12 Answers12

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