Check if a string contains only digits in ruby

Question

I have a string which is passed as a parameter to a function. Here, I want to check if the string contains only numbers. So I had a check like below:

def check_string(string)
  result = false
  if string.to_i.to_s.eql? string
    result =  true
  end
  result
end

But the problem arises when a string starts with 0. In that case, a false is returned.

check_string('123')  #=> true
check_string('0123') #=> false

How can I solve this issue?

See also http://stackoverflow.com/questions/5661466/test-if-string-is-a-number-in-ruby-on-rails/5661695 — Mark Thomas, Apr 21 '17 at 12:44

score 43 · Accepted Answer · edited May 07 '19 at 10:57

43

You can try the following

def check_string(string)
  string.scan(/\D/).empty?
end

It would be truthy if string contains only digits or if it is an empty string. Otherwise returns false.

edited May 07 '19 at 10:57

rmcsharry

5,363
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answered Sep 28 '16 at 09:34

Aleksey

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4

This is smart. You can also go with a variation of your answer and @Stefan's suggestion `string.scan(/^\d+$/).any?` which reads quite nicely I think. – Sagar Pandya Sep 28 '16 at 12:24
As for me the answer as it is now is more first-look-understandable ;) Just looking for nondigit symbol. If there isn't one - check has passed. – Aleksey Sep 28 '16 at 12:57

score 6 · Answer 2 · answered Sep 14 '18 at 11:55

A number can be negative, or a float. So if these are allowed, consider this solution:

def is_numberic?(str)
    str == "#{str.to_f}" || str == "#{str.to_i}"
end

some input which evaluate to true

pry(main)> is_numberic? '5'
=> true
pry(main)> is_numberic? '58127721'
=> true
pry(main)> is_numberic? '58127721.737673'
=> true
pry(main)> is_numberic? '0'
=> true
pry(main)> is_numberic? '1818'
=> true
pry(main)> is_numberic? '0.1'
=> true
pry(main)> is_numberic? '0.0'
=> true
pry(main)> is_numberic? '11.29'
=> true
pry(main)> is_numberic? '-0.12'
=> true
pry(main)> is_numberic? '-29'
=> true

the input which evaluate to false

pry(main)> is_numberic? '10 years'
=> false
pry(main)> is_numberic? '01'
=> false
pry(main)> is_numberic? '00'
=> false
pry(main)> is_numberic? '0.10'
=> false
pry(main)> is_numberic? ''
=> false

As you can see, there're several cases which probably should be supported, eg '0.10', but are not. In this case, the permitted input is '0.1'.

Cary Swoveland · Answer 3 · 2019-07-22T20:31:00.587

5

def check_string(str)
  str !~ /\D/
end

check_string '123'
  #=> true
check_string ''
  #=> true
check_string '1a2'
  #=> false

edited Jul 22 '19 at 20:31

answered Sep 30 '16 at 07:29

Cary Swoveland

106,649
6
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Kaiizer · Answer 4 · 2023-01-17T15:14:40.663

this is my proposition for detecting if it's a float number

def check(string)
  scan = string.scan(/\D/)
  scan.size == 0 || (scan.size == 1 && scan.first == ".") # or "," depend on your separator
end

example of use:

check("123") => true
check("12.3") => true
check("12e3") => false
check("12.3.2") => false

EDIT: 2023 After some years i see this is the most compact solution:

def check_string(str)
  str.scan(/\D/).empty?
end

Andrey Deineko · Answer 5 · 2016-09-28T10:54:46.937

1

You can use Regexp for it:

def check_string(string)
  raise 'Empty string passed' if string.empty?

  /\A\d+\z/ === string
end

check_string '123'
#=> true
check_string '0123'
#=> true
check_string '0'
#=> true

edited Sep 28 '16 at 10:54

answered Sep 28 '16 at 09:40

Andrey Deineko

51,333
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1

Wouldn't work for `string = '0'` – why not simply `/^\d+$/` or `/\A\d+\z/`? – Stefan Sep 28 '16 at 10:14
@Stefan `/^\d+$/` makes perfect sense! – Andrey Deineko Sep 28 '16 at 10:16
2

@AndreyDeineko This fails the premise for the string "foobar\n123" since your regex matches here. You actually want to use `/\A\d+\z/`. – Holger Just Sep 28 '16 at 10:53
seems this could be simplified to just `string =~ /\A\d+\z/ ? true : false` this handles all the cases and will return false on an empty string since it contains no numbers. – engineersmnky Sep 28 '16 at 15:01

score 1 · Answer 6 · answered Jan 07 '19 at 21:37

1

We can also use the "match" function to do this.

"1234".match(/\D/)
#=> nil
"1234foo".match(/\D/)
#=> #<MatchData "f">

match (String) - APIdock

answered Jan 07 '19 at 21:37

Tilak M Divakar

101
1
5

score 0 · Answer 7 · answered Feb 17 '22 at 12:47

0

I think we should use the regex to find this.

it will work for the below scenarios
"3.0"
"av3"
"3"

is_numeric = false if option.option.match?(/[^0-9.]/)

answered Feb 17 '22 at 12:47

Iqbal Khan

4,587
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option.option is your preferred string? – RixTheTyrunt May 12 '22 at 11:11

score -2 · Answer 8 · answered Mar 19 '20 at 15:12

If anyone is searching for another way to determine if string is numeric -> is to use "is_a? Numeric". Is_a? reference documentation

"namaste".is_a? Numeric
=> false

6.is_a? Numeric
=> true

str1 = "foo"
str2 = 9

str1.is_a? Numeric
=> false
str2.is_a? Numeric
=> true

You can also use:

7.is_a?(Numeric)
=> true

"too".is_a?(Numeric)
=> false

Basically it's determining if a class is a type of class object. I just found this and thought I would share.

Your `str2` is not a string. Try this with `str2 = "9"` and see if it works (It does not). — IMP1, Mar 19 '20 at 15:15

Check if a string contains only digits in ruby

8 Answers8