# Check numbers

**URL:** <https://www.ruby-forum.com/t/check-numbers/113616>\
**Category:** Rails\
**Created:** [September 2, 2007, 11:38pm UTC](https://www.ruby-forum.com/t/check-numbers/113616 "2007-09-02T23:38:56Z")\
**Posts on this page:** 9\
**Page:** 1

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**Author:** ![shafi](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/439d5e/32.png) [@shafi](https://www.ruby-forum.com/u/shafi)\
**Post date:** [September 2, 2007, 11:38pm UTC](https://www.ruby-forum.com/t/check-numbers/113616/1 "2007-09-02T23:38:56Z")

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Hello people,

how to check string to know if it is number or not.

ex:  
isnumber(‘text’) ==\> false  
isnumber(‘22’) ==\> true

Thanks.

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<div class="post-metadata">

**Author:** ![shafi](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/439d5e/32.png) [@shafi](https://www.ruby-forum.com/u/shafi)\
**Post date:** [September 3, 2007, 1:07am UTC](https://www.ruby-forum.com/t/check-numbers/113616/2 "2007-09-03T01:07:05Z")

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There are a few ways to do this. I’ll give some examples for checking  
if the string is an integer, which might be sufficient for you.  
Checking for floats, rationals, etc will be more complex.

# is\_integer.rb

class String  
def is\_integer?  
!self.empty? && self =~ /\A\d+\Z/ # not the empty string and  
containing only one or more digits  
end

def is\_integer2?  
!self.empty? && Integer(self) rescue false # not the empty string  
and capable of being coerced by Integer()  
end

def is\_integer3?  
!self.empty? && self.scan(/\D/).empty? # not the empty string and  
containing no non-digit characters  
end  
end

Here is one benchmark:

["", “1”, “123”, “foo”, “foo123”].each { |string| string.is\_integer?}

# (n = 10,000)

```
            user system total real
regex: 0.070000 0.000000 0.070000 ( 0.065365)

```

Integer(): 0.580000 0.040000 0.620000 ( 0.620194)  
scan: 0.150000 0.000000 0.150000 ( 0.150243)

Using Integer and rescuing the thrown exception is quick for integer  
strings but grossly inefficient for non-integer strings (as expected).  
The regex is fastest all-around of the three examples given and  
benchmarking shows that short-circuiting on the empty string really  
speeds up the special case of “”.is\_integer?

Feel free to suggest other implementations. I’ll put the lib, unit  
test and benchmark files on my blog for you to use. (As soon as I get  
my blog up and running. Probably tomorrow. Stay tuned.) Until then,  
here’s the benchmark used above:

# is\_integer\_bm.rb

require ‘benchmark’  
require ‘is\_integer’ # your is\_integer.rb where the extension to  
String is located

STRINGS = ["", “1”, “123”, “foo”, “foo123”]

def bench\_total  
n = 10000  
puts “\n”  
print STRINGS.inspect  
print".each { |string| string.is\_integer?}"  
print " # (n = 10,000)\n"  
Benchmark.bm(10) do |x|  
x.report(" regex:") { n.times { STRINGS.each{ |str|  
str.is\_integer? } } }  
x.report(“Integer():”) { n.times { STRINGS.each{ |str|  
str.is\_integer2? } } }  
x.report(" scan:") { n.times { STRINGS.each{ |str|  
str.is\_integer3? } } }  
end  
end

bench\_total

Rein

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<div class="post-metadata">

**Author:** ![shafi](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/439d5e/32.png) [@shafi](https://www.ruby-forum.com/u/shafi)\
**Post date:** [September 3, 2007, 8:17am UTC](https://www.ruby-forum.com/t/check-numbers/113616/3 "2007-09-03T08:17:36Z")

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faisal,

The ternary here is useless as == already returns a boolean, and this  
is also integer only rather than any number, so changing your method  
to:

class String  
def is\_integer?  
self.to\_i.to\_s == self  
end  
end

and adding it to the benchmark, we get:

["", “1”, “123”, “foo”, “foo123”].each { |string| string.is\_integer?}

# (n = 10,000)

```
            user system total real
regex: 0.070000 0.000000 0.070000 ( 0.069953)

```

Integer(): 0.580000 0.040000 0.620000 ( 0.635358)  
scan: 0.150000 0.000000 0.150000 ( 0.172896)  
to\_i.to\_s: 0.150000 0.000000 0.150000 ( 0.157933)

Or roughly equal to the scan method but still about half as fast as  
the regex. So far you’re in second place. Thanks for playing 😉

Incidentally faisal’s method does actually work as a test for integer-  
ness. (There has to be a better word…) My only issue with it is that  
it is not very intention revealing. Then again, neither is the regex  
if you aren’t familiar with regexen.

---

<div class="post-metadata">

**Author:** ![shafi](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/439d5e/32.png) [@shafi](https://www.ruby-forum.com/u/shafi)\
**Post date:** [September 3, 2007, 8:22am UTC](https://www.ruby-forum.com/t/check-numbers/113616/4 "2007-09-03T08:22:37Z")

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Incidentally, the regex method without the check for empty? is  
actually slightly faster overall than with the check for empty? so the  
most performant method so far is:

class String  
def is\_integer?  
self =~ /\A\d+\Z/  
end  
end

---

<div class="post-metadata">

**Author:** ![shafi](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/439d5e/32.png) [@shafi](https://www.ruby-forum.com/u/shafi)\
**Post date:** [September 3, 2007, 7:58am UTC](https://www.ruby-forum.com/t/check-numbers/113616/5 "2007-09-03T07:58:32Z")

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def isnumber(string)  
string.to\_i.to\_s == string ? true : false  
end

-faisal

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<div class="post-metadata">

**Author:** ![shafi](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/439d5e/32.png) [@shafi](https://www.ruby-forum.com/u/shafi)\
**Post date:** [September 3, 2007, 9:23am UTC](https://www.ruby-forum.com/t/check-numbers/113616/6 "2007-09-03T09:23:44Z")

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rewritten in a object oriented manner:

class String  
def is\_integer?  
self.to\_i \>= 1  
end  
end

“0”.is\_integer? #=\> false  
“-123”.is\_integer? #=\> false

'fraid not.

You did, however, remind me about negative integers.

class String  
def is\_integer?  
self =~ /\A-?\d+\Z/  
end  
end

and the scan method won’t work on negative integers. Whoops!

On Sep 3, 2:09 am, Jamal S. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)

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<div class="post-metadata">

**Author:** ![shafi](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/439d5e/32.png) [@shafi](https://www.ruby-forum.com/u/shafi)\
**Post date:** [September 4, 2007, 4:43am UTC](https://www.ruby-forum.com/t/check-numbers/113616/7 "2007-09-04T04:43:44Z")

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For posterity: [http://reinh.com/2007/9/4/string-is\_integer](http://reinh.com/2007/9/4/string-is_integer)

Rein

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<div class="post-metadata">

**Author:** ![shafi](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/439d5e/32.png) [@shafi](https://www.ruby-forum.com/u/shafi)\
**Post date:** [September 4, 2007, 6:35am UTC](https://www.ruby-forum.com/t/check-numbers/113616/8 "2007-09-04T06:35:50Z")

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On Sep 3, 2007, at 2:17 AM, removed\_email\_address@domain.invalid wrote:

> The ternary here is useless as == already returns a boolean

i could argue that it’s mostly for readability, although having used  
a ternary in the first place i could argue that i should have an  
entire chorus lined up to laugh at the code.

-faisal

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<div class="post-metadata">

**Author:** ![shafi](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/439d5e/32.png) [@shafi](https://www.ruby-forum.com/u/shafi)\
**Post date:** [September 3, 2007, 9:09am UTC](https://www.ruby-forum.com/t/check-numbers/113616/9 "2007-09-03T09:09:20Z")

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Well, I would do this as follow in PHP

@num = @as.to\_i

if @num \>= 1  
puts “is number”  
end

Would this work?