如何检查一个值是否是一个数字？

我想简单地检查一下从表单文本字段返回的值是否是一个数字，例如: 12、12.5或12.75。是否有一种简单的方法来检查这一点，特别是如果值是作为 param提取的？

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小开

You can use

12.is_a? Numeric

(Numeric will work for integers and floats.)

If it arrives as a string that might contain a representation of a valid number, you could use

class String
def valid_float?
true if Float self rescue false
end
end

and then '12'.valid_float? will return true if you can convert the string to a valid float (e.g. with to_f).

小开

You can add a:

validates_numericality_of :the_field

in your model.

See: http://api.rubyonrails.org/classes/ActiveRecord/Validations/ClassMethods.html#M002172

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最佳答案

Just regexp it, it's trivial, and not worth thinking about beyond that:

v =~ /\A[-+]?[0-9]*\.?[0-9]+\Z/

(Fixed as per Justin's comment)

小开

I would suggest this one

def is_a_number?(str)
!!(Float(str) rescue false)
end


> is_a_number?(1)
=> true


> is_a_number?(1.1)
=> true


> is_a_number?('1')
=> true


> is_a_number?('1.1')
=> true


> is_a_number?('a')
=> false


> is_a_number?(nil)
=> false

小开

I usually just use Integer and Float these days.

1.9.2p320 :001 > foo = "343"
=> "343"
1.9.2p320 :003 > goo = "fg5"
=> "fg5"


1.9.2p320 :002 > Integer(foo) rescue nil
=> 343
1.9.2p320 :004 > Integer(goo) rescue nil
=> nil


1.9.2p320 :005 > Float(foo) rescue nil
=> 343.0
1.9.2p320 :006 > Float(goo) rescue nil
=> nil

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irb(main):005:0> 1.1.is_a? Numeric
=> true
irb(main):006:0> 1.is_a? Numeric
=> true
irb(main):007:0> 'asd'.is_a? Numeric
=> false

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String values always convert to 0 with .to_i

[14] pry(main)> 'Apple'.to_i > 0
=> false


[15] pry(main)> '101'.to_i > 0
=> true

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Just convert string twice:

num = '12'
num == num.to_i.to_s
#=> true


num = '3re'
num == num.to_i.to_s
#=> false

小开

There was answer with Kernel#Float

But this variant is used with exception: false key and double bang to return boolean

class String
def number?
!!Float(self, exception: false)
end
end