blocks|key|1145365|text|在显示时，您可以使用(例如)|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1145366|>>+'%25.2f'+%25+2.3465
=>+"2.35"|code-block|syntax|javascript|1145367|如果你想四舍五入地存储它，你可以使用|1145368|>>+(2.3465*100).round+/+100.0
=>+2.35|1145369|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

When displaying, you can use (for example)

<pre><code>&gt;&gt; '%.2f' % 2.3465
=&gt; "2.35"
</code></pre>

If you want to store it rounded, you can use 

<pre><code>&gt;&gt; (2.3465*100).round / 100.0
=&gt; 2.35
</code></pre>

blocks|key|1145382|text|那(2.3465*100).round()/100.0呢？|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1145383|entityMap^0|1|Q|0^^$0|@$1|2|3|4|5|6|7|H|8|@$9|I|A|J|B|C]]|D|@]|E|$]]|$1|F|3|-4|5|6|7|K|8|@]|D|@]|E|$]]]|G|$]]

what about <code>(2.3465*100).round()/100.0</code>?

blocks|key|1360445|text|将包含要舍入到的小数位数的参数传递给round|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1360446|>>+2.3465.round
=>+2
>>+2.3465.round(2)
=>+2.35
>>+2.3465.round(3)
=>+2.347|code-block|syntax|javascript|1360447|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Pass an argument to round containing the number of decimal places to round to

<pre><code>&gt;&gt; 2.3465.round
=&gt; 2
&gt;&gt; 2.3465.round(2)
=&gt; 2.35
&gt;&gt; 2.3465.round(3)
=&gt; 2.347
</code></pre>

blocks|key|1360465|text|你可以在Float类中添加一个方法，这是我从stackoverflow学到的：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1360466|class+Float
++++def+precision(p)
++++++++#+Make+sure+the+precision+level+is+actually+an+integer+and+>+0
++++++++raise+ArgumentError,+"#{p}+is+an+invalid+precision+level.+Valid+ranges+are+integers+>+0."+unless+p.class+==+Fixnum+or+p+<+0
++++++++#+Special+case+for+0+precision+so+it+returns+a+Fixnum+and+thus+doesn't+have+a+trailing+.0
++++++++return+self.round+if+p+==+0
++++++++#+Standard+case++
++++++++return+(self+*+10**p).round.to_f+/+10**p
++++end
end|code-block|syntax|javascript|1360467|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

You can add a method in Float Class, I learnt this from stackoverflow:

<pre><code>class Float
 def precision(p)
 # Make sure the precision level is actually an integer and &gt; 0
 raise ArgumentError, "#{p} is an invalid precision level. Valid ranges are integers &gt; 0." unless p.class == Fixnum or p &lt; 0
 # Special case for 0 precision so it returns a Fixnum and thus doesn't have a trailing .0
 return self.round if p == 0
 # Standard case 
 return (self * 10**p).round.to_f / 10**p
 end
end
</code></pre>

blocks|key|1145474|text|def+rounding(float,precision)
++++return+((float+*+10**precision).round.to_f)+/+(10**precision)
end|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|1145475|unstyled|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|G|8|@]|9|@]|A|$B|C]]|$1|D|3|-4|5|E|7|H|8|@]|9|@]|A|$]]]|F|$]]

<pre><code>def rounding(float,precision)
 return ((float * 10**precision).round.to_f) / (10**precision)
end
</code></pre>

blocks|key|1360519|text|对于ruby+1.8.7，您可以在代码中添加以下内容：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1360520|class+Float
++++alias+oldround:round
++++def+round(precision+=+nil)
++++++++if+precision.nil?
++++++++++++return+self
++++++++else
++++++++++++return+((self+*+10**precision).oldround.to_f)+/+(10**precision)
++++++++end+
++++end+
end|code-block|syntax|javascript|1360521|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

For ruby 1.8.7 you could add the following to your code:

<pre><code>class Float
 alias oldround:round
 def round(precision = nil)
 if precision.nil?
 return self
 else
 return ((self * 10**precision).oldround.to_f) / (10**precision)
 end 
 end 
end
</code></pre>

blocks|key|1145530|text|如果您只需要显示它，我会使用number_with_precision助手。如果您需要在其他地方使用它，我会使用Steve+Weet指出的round方法|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1145531|entityMap|0|LINK|mutability|MUTABLE|url|http://api.rubyonrails.org/classes/ActionView/Helpers/NumberHelper.html#method-i-number_with_precision^0|1X|5|E|L|0|0^^$0|@$1|2|3|4|5|6|7|N|8|@$9|O|A|P|B|C]]|D|@$9|Q|A|R|1|S]]|E|$]]|$1|F|3|-4|5|6|7|T|8|@]|D|@]|E|$]]]|G|$H|$5|I|J|K|E|$L|M]]]]

If you just need to display it, I would use the <a href="http://api.rubyonrails.org/classes/ActionView/Helpers/NumberHelper.html#method-i-number_with_precision" rel="nofollow">number_with_precision</a> helper.
If you need it somewhere else I would use, as Steve Weet pointed, the <code>round</code> method

blocks|key|1145547|text|还可以将负数作为参数提供给round方法，以舍入到最接近的10、100的倍数，依此类推。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1145548|#+Round+to+the+nearest+multiple+of+10.+
12.3453.round(-1)+++++++#+Output:+10

#+Round+to+the+nearest+multiple+of+100.+
124.3453.round(-2)++++++#+Output:+100|code-block|syntax|javascript|1145549|entityMap^0|D|5|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@$9|N|A|O|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|P|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|Q|8|@]|D|@]|E|$]]]|L|$]]

You can also provide a negative number as an argument to the <code>round</code> method to round to the nearest multiple of 10, 100 and so on.

<pre><code># Round to the nearest multiple of 10. 
12.3453.round(-1) # Output: 10

# Round to the nearest multiple of 100. 
124.3453.round(-2) # Output: 100
</code></pre>

blocks|key|1360606|text|您可以使用它来四舍五入到一个精度。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1360607|//to_f+is+for+float

salary=+2921.9121
puts+salary.to_f.round(2)+//+to+2+decimal+place+++++++++++++++++++

puts+salary.to_f.round()+//+to+3+decimal+place++++++++++|code-block|syntax|javascript|1360608|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

you can use this for rounding to a precison..

<pre><code>//to_f is for float

salary= 2921.9121
puts salary.to_f.round(2) // to 2 decimal place 

puts salary.to_f.round() // to 3 decimal place 
</code></pre>

I'm having problems rounding. I have a float, which I want to round to the hundredth of a decimal. However, I can only use <code>.round</code> which basically turns it into an int, meaning <code>2.34.round # =&gt; 2.</code> Is there a simple effect way to do something like <code>2.3465 # =&gt; 2.35</code>

Ruby: Rounding float in Ruby

我在四舍五入时遇到了问题。我有一个浮点数，我想把它四舍五入到小数点的百分之一。然而，我只能使用.round，它基本上将它转换为一个整数，这意味着2.34.round # => 2.有没有一种简单有效的方法来做像2.3465 # => 2.35这样的事情

问Ruby: Ruby中的舍入浮点数
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