How to test if a string is basically an integer in quotes using Ruby

Question

I need a function  is an integer  where    12  is an integer  returns true   blah  is an integer  returns false    How can I do this in Ruby   I would write a regex but I m assuming there is a helper for this that I am not aware of

User · Answer

For more generalised cases  including numbers with decimal point   you can try the following method   def number  obj    obj   obj to s unless obj is a  String     A  -   d      d     z  match obj  end   You can test this method in an irb session    irb   gt  gt  number  7    gt    lt MatchData  7  1 nil gt   gt  gt    number  7    gt  true  gt  gt  number  -Math  PI    gt    lt MatchData  -3 141592653589793  1   141592653589793  gt   gt  gt    number  -Math  PI    gt  true  gt  gt  number   hello world     gt  nil  gt  gt    number   hello world     gt  false   For a detailed explanation of the regex involved here  check out this blog article

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Personally I like the exception approach although I would make it a little more terse   class String   def integer  str        Integer str  rescue false   end end   However  as others have already stated  this doesn t work with Octal strings

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This might not be suitable for all cases simplely using    12  to i     gt  12  blah  to i   gt  0   might also do for some   If it s a number and not 0 it will return a number  If it returns 0 it s either a string or 0

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Well  here s the easy way   class String   def is integer      self to i to s    self   end end   gt  gt   12  is integer    gt  true  gt  gt   blah  is integer    gt  false   I don t agree with the solutions that provoke an exception to convert the string - exceptions are not control flow  and you might as well do it the right way  That said  my solution above doesn t deal with non-base-10 integers  So here s the way to do with without resorting to exceptions     class String     def integer                                      In descending order of likeliness             -    1-9   0-9          decimal           0 0-7                    octal           0x 0-9A-Fa-f             hexadecimal           0b 01                    binary         each do  match pattern          return true if self    match pattern       end       return false     end   end

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12  match     d             true  1 2  match     d            false  dfs2  match     d           false  13422  match     d          true

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Ruby 2 4 has Regexp match    with a     def integer  str      A  -   d  z  match  str end   For older Ruby versions  there s Regexp      And although direct use of the case equality operator should generally be avoided  it looks very clean here   def integer  str      A  -   d  z      str end  integer   123       true integer   -123      true integer    123      true  integer   a123      false integer   123b      false integer   1 n2      false

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class String   def integer      Integer self      return true   rescue ArgumentError     return false   end end    It isn t prefixed with is   I find that silly on questionmark methods  I like  04  integer  a lot better than  foo  is integer   It uses the sensible solution by sepp2k  which passes for  01  and such  Object oriented  yay

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You can use Integer str  and see if it raises   def is num  str      Integer str  rescue ArgumentError  TypeError   false end   It should be pointed out that while this does return true for  01   it does not for  09   simply because 09 would not be a valid integer literal  If that s not the behaviour you want  you can add 10 as a second argument to Integer  so the number is always interpreted as base 10

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I prefer    config initializers string rb  class String   def number      Integer self  is a  Integer    rescue ArgumentError  TypeError     false   end end   and then     218  pry main  gt   123123123  number    gt  true  220  pry main  gt   123 123 123  gsub          number    gt  true  222  pry main  gt   123 123 123  number    gt  false   or check phone number      34 123 456 789 2  gsub          number

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I like the following  straight forward   def is integer  str    str to i    0    str     0     str     -0  end  is integer   123     gt  true  is integer   sdf     gt  false  is integer   -123     gt  true  is integer   0     gt  true  is integer   -0     gt  true   Careful though   is integer   123sdfsdf     gt  true

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One liner in string rb  def is integer   true if Integer self  rescue false end

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The Best and Simple way is using Float  val   Float  234  rescue nil  Float  234  rescue nil    gt  234 0  Float  abc  rescue nil    gt  nil  Float  234abc  rescue nil    gt  nil  Float nil rescue nil    gt  nil  Float    rescue nil    gt  nil   Integer is also good but it will return 0 for Integer nil

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A much simpler way could be      D    match  1221   nil     gt  true    D    match  1a221   nil     gt  false    D    match  01221   nil     gt  true

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Ruby 2 6 0 enables casting to an integer without raising an exception  and will return nil if the cast fails  And since nil mostly behaves like false in Ruby  you can easily check for an integer like so   if Integer my var  exception  false      do something if my var can be cast to an integer end

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def isint str      return    str       -    1-9   0-9          end

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You can use regular expressions  Here is the function with  janm s suggestions   class String     def is i            self      A -    0-9   z       end end   An edited version according to comment from  wich   class String     def is i           A -    d  z      self     end end   In case you only need to check positive numbers     if    A d  z  match string to check         Is not a positive number   else        Is all good   continue   end

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You can do a one liner   str       int   Integer str  rescue nil  if int   int times   i  p i  end   or even  int   Integer str  rescue false   Depending on what you are trying to do you can also directly use a begin end block with rescue clause   begin   str         i   Integer str     i times do  j      puts j   end rescue ArgumentError   puts  Not an int  doing something else  end

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Here s my solution      initializers string rb class String   IntegerRegex       d        def integer        self match IntegerRegex    end end    any model or controller rb  12345  integer    true  asd34  integer    false   And here s how it works        d    is regex expression for finding digits in any string  You can test your regex expressions and results at http   rubular com   We save it in a constant IntegerRegex to avoid unnecessary memory allocation everytime we use it in the method  integer  is an interrogative method which should return true or false  match is a method on string which matches the occurrences as per the given regex expression in argument and return the matched values or nil     converts the result of match method into equivalent boolean  And declaring the method in existing String class is monkey patching  which doesn t change anything in existing String functionalities  but just adds another method named integer  on any String object

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Expanding on  rado s answer above one could also use a ternary statement to force the return of true or false booleans without the use of double bangs  Granted  the double logical negation version is more terse  but probably harder to read for newcomers  like me    class String   def is i       self      A -    0-9   z    true   false   end end

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I m not sure if this was around when this question is asked but  for anyone that stumbles across this post  the simplest way is   var    12  var is a  Integer    returns false var is a  String    returns true  var   12 var is a  Integer    returns true var is a  String    returns false    is a  will work with any object

[ruby] How to test if a string is basically an integer in quotes using Ruby

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