Test if string is a number in Ruby on Rails

Question

I have the following in my application controller   def is number  object    true if Float object  rescue false end   and the following condition in my controller   if mystring is number   end   The condition is throwing an undefined method error  I m guessing I ve defined is number in the wrong place

User · Answer

If you prefer not to use exceptions as part of the logic, you might try this:

class String
   def numeric?
    !!(self =~ /^-?\d+(\.\d*)?$/)
  end
end

Or, if you want it to work across all object classes, replace class String with class Object an convert self to a string: !!(self.to_s =~ /^-?\d+(\.\d*)?$/)

User · Answer

Here s a benchmark for common ways to address this problem  Note which one you should use probably depends on the ratio of false cases expected    If they are relatively uncommon casting is definitely fastest  If false cases are common and you are just checking for ints  comparison vs a transformed state is a good option  If false cases are common and you are checking floats  regexp is probably the way to go   If performance doesn t matter use what you like   -   Integer checking details     1 9 3-p448     Calculating -------------------------------------                   cast     57485 i 100ms              cast fail      5549 i 100ms                   to s     47509 i 100ms              to s fail     50573 i 100ms                 regexp     45187 i 100ms            regexp fail     42566 i 100ms   -------------------------------------------------                   cast  2353703 4    4 9   i s -   11726940 in   4 998270s              cast fail    65590 2    4 6   i s -     327391 in   5 003511s                   to s  1420892 0    6 8   i s -    7078841 in   5 011462s              to s fail  1717948 8    6 0   i s -    8546837 in   4 998672s                 regexp  1525729 9    7 0   i s -    7591416 in   5 007105s            regexp fail  1154461 1    5 5   i s -    5788976 in   5 035311s  require  benchmark ips   int    220000  bad int    22 to 2   Benchmark ips do  x    x report  cast   do     Integer int  rescue false   end    x report  cast fail   do     Integer bad int  rescue false   end    x report  to s   do     int to i to s    int   end    x report  to s fail   do     bad int to i to s    bad int   end    x report  regexp   do     int       d      end    x report  regexp fail   do     bad int       d      end end   Float checking details     1 9 3-p448     Calculating -------------------------------------                   cast     47430 i 100ms              cast fail      5023 i 100ms                   to s     27435 i 100ms              to s fail     29609 i 100ms                 regexp     37620 i 100ms            regexp fail     32557 i 100ms   -------------------------------------------------                   cast  2283762 5    6 8   i s -   11383200 in   5 012934s              cast fail    63108 8    6 7   i s -     316449 in   5 038518s                   to s   593069 3    8 8   i s -    2962980 in   5 042459s              to s fail   857217 1    10 0   i s -    4263696 in   5 033024s                 regexp  1383194 8    6 7   i s -    6884460 in   5 008275s            regexp fail   723390 2    5 8   i s -    3613827 in   5 016494s  require  benchmark ips   float    12 2312  bad float    22 to 2   Benchmark ips do  x    x report  cast   do     Float float  rescue false   end    x report  cast fail   do     Float bad float  rescue false   end    x report  to s   do     float to f to s    float   end    x report  to s fail   do     bad float to f to s    bad float   end    x report  regexp   do     float       -    0-9      0-9       end    x report  regexp fail   do     bad float       -    0-9      0-9       end end

User · Answer

As Jakob S suggested in his answer  Kernel Float can be used to validate numericality of the string  only thing that I can add is one-liner version of that  without using rescue block to control flow  which is considered as a bad practice sometimes    Float my string  exception  false  present

User · Answer

As of Ruby 2 6 0  the numeric cast-methods have an optional exception-argument  1   This enables us to use the built-in methods without using exceptions as control flow   Float  x       gt  ArgumentError  invalid value for Float     x   Float  x   exception  false      gt  nil   Therefore  you don t have to define your own method  but can directly check variables like e g   if Float my var  exception  false      do something if my var is a float end

User · Answer

Relying on the raised exception is not the fastest  readable nor reliable solution  I d do the following    my string should       0-9

User · Answer

In rails 4  you need to put  require File expand path        lib     FILE        ext string  in your config application rb

User · Answer

Create is number  Method   Create a helper method    def is number  string   true if Float string  rescue false end   And then call it like this   my string    12 34   is number   my string       gt  true   Extend String Class   If you want to be able to call is number  directly on the string instead of passing it as a param to your helper function  then you need to define is number  as an extension of the String class  like so   class String   def is number      true if Float self  rescue false   end end   And then you can call it with   my string is number      gt  true

User · Answer

no you re just using it wrong  your is number  has an argument  you called it without the argument  you should be doing is number  mystring

User · Answer

How dumb is this solution   def is number  i    begin     i 0    i   rescue TypeError     false   end end

User · Answer

Tl dr  Use a regex approach  It is 39x faster than the rescue approach in the accepted answer and also handles cases like  1 000   def regex is number  string   no commas    string gsub            matches   no commas match  -  d       d        if  matches nil   amp  amp  matches size    1  amp  amp  matches 0     no commas     true   else     false   end end   --  The accepted answer by  Jakob S works for the most part  but catching exceptions can be really slow  In addition  the rescue approach fails on a string like  1 000     Let s define the methods   def rescue is number  string   true if Float string  rescue false end  def regex is number  string   no commas    string gsub            matches   no commas match  -  d       d        if  matches nil   amp  amp  matches size    1  amp  amp  matches 0     no commas     true   else     false   end end   And now some test cases   test cases       true   gt    5 5    23    -123    1 234 123      false   gt    hello    99designs     123 456-7890       And a little code to run the test cases   test cases each do  expected answer  cases    cases each do  test case      if rescue is number  test case     expected answer       puts    rescue is number  got   test case  wrong        else       puts  rescue is number  got   test case  right      end      if regex is number  test case     expected answer       puts    regex is number  got   test case  wrong        else       puts  regex is number  got   test case  right      end     end end   Here is the output of the test cases   rescue is number  got 5 5 right regex is number  got 5 5 right rescue is number  got 23 right regex is number  got 23 right rescue is number  got -123 right regex is number  got -123 right   rescue is number  got 1 234 123 wrong   regex is number  got 1 234 123 right rescue is number  got hello right regex is number  got hello right rescue is number  got 99designs right regex is number  got 99designs right rescue is number  got  123 456-7890 right regex is number  got  123 456-7890 right   Time to do some performance benchmarks   Benchmark ips do  x     x report  rescue     test cases values flatten each    c  rescue is number  c       x report  regex     test cases values flatten each    c  regex is number  c        x compare  end   And the results   Calculating -------------------------------------               rescue   128 000  i 100ms                regex     4 649k i 100ms -------------------------------------------------               rescue      1 348k    16 8   i s -      6 656k                regex     52 113k     7 8   i s -    260 344k  Comparison                 regex     52113 3 i s               rescue      1347 5 i s - 38 67x slower

User · Answer

this is how i do it  but i think too there must be a better way  object to i to s    object    object to f to s    object

User · Answer

class String   def numeric      return true if self      A d  Z      true if Float self  rescue false   end end    p  1  numeric       gt  true p  1 2  numeric      gt  true p  5 4e-29  numeric      gt  true p  12e20  numeric    true p  1a  numeric      gt  false p  1 2 3 4  numeric      gt  false

User · Answer

use the following function   def is numeric  val     return val try  to f  try  to s     val end   so    is numeric   1 2f    false  is numeric   1 2    true  is numeric   12f    false  is numeric   12    true

[ruby-on-rails] Test if string is a number in Ruby on Rails

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