blocks|key|1631770|text|你必须调用函数对象的方法"+call“：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1631771|weight+=+weightf.call(+dist+)|code-block|syntax|javascript|1631772|编辑:正如评论中所解释的，这种方法是错误的。如果你使用的是Procs而不是普通函数，这将会起作用。|1631773|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|L|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

You have to call the method "call" of the function object:

<pre><code>weight = weightf.call( dist )
</code></pre>

EDIT: as explained in the comments, this approach is wrong. It would work if you're using Procs instead of normal functions.

blocks|key|1417045|text|正常的Ruby方法是使用块。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1417046|所以它应该是这样的：|1417047|def+weightedknn(+data,+vec1,+k+=+5+)
++foo
++weight+=+yield(+dist+)
++foo
end|code-block|syntax|javascript|1417048|它的用法如下：|1417049|weightenknn(+data,+vec1+)+{+%7Cdist%7C+gaussian(+dist+)+}|1417050|此模式在Ruby中广泛使用。|1417051|entityMap^0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|R|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|S|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|T|8|@]|9|@]|A|$]]|$1|K|3|L|5|F|7|U|8|@]|9|@]|A|$G|H]]|$1|M|3|N|5|6|7|V|8|@]|9|@]|A|$]]|$1|O|3|-4|5|6|7|W|8|@]|9|@]|A|$]]]|P|$]]

The normal Ruby way to do this is to use a block.

So it would be something like:

<pre><code>def weightedknn( data, vec1, k = 5 )
 foo
 weight = yield( dist )
 foo
end
</code></pre>

And used like:

<pre><code>weightenknn( data, vec1 ) { |dist| gaussian( dist ) }
</code></pre>

This pattern is used extensively in Ruby.

blocks|key|1417143|text|引用块和Procs的注释是正确的，因为它们在Ruby中更常见。但是如果你愿意，你可以传递一个方法。调用method来获取方法，调用.call来调用它：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1417144|def+weightedknn(+data,+vec1,+k+=+5,+weightf+=+method(:gaussian)+)
++...
++weight+=+weightf.call(+dist+)
++...
end|code-block|syntax|javascript|1417145|entityMap^0|1F|6|1T|5|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@$9|N|A|O|B|C]|$9|P|A|Q|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|R|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|S|8|@]|D|@]|E|$]]]|L|$]]

The comments referring to blocks and Procs are correct in that they are more usual in Ruby. But you can pass a method if you want. You call <code>method</code> to get the method and <code>.call</code> to call it:

<pre><code>def weightedknn( data, vec1, k = 5, weightf = method(:gaussian) )
 ...
 weight = weightf.call( dist )
 ...
end
</code></pre>

blocks|key|1632045|text|我建议使用“与”符号来访问函数中的命名块。遵循this+article中给出的建议，您可以编写类似这样的代码(这是我的工作程序中的一部分)：|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1632046|++#+Returns+a+valid+hash+for+html+form+select+element,+combined+of+all+entities
++#+for+the+given+%2Bmodel%2B,+where+only+id+and+name+attributes+are+taken+as
++#+values+and+keys+correspondingly.+Provide+block+returning+boolean+if+you
++#+need+to+select+only+specific+entities.
++#
++#+*+*Args*++++:
++#+++-+%2Bmodel%2B+->+ORM+interface+for+specific+entities'
++#+++-+%2B&cond%2B+->+block+{%7Cx%7C+boolean},+filtering+entities+upon+iterations
++#+*+*Returns*+:
++#+++-+hash+of+{entity.id+=>+entity.name}
++#
++def+make_select_list(+model,+&cond+)
++++cond+%7C%7C=+proc+{+true+}+#+cond+defaults+to+proc+{+true+}
++++#+Entities+filtered+by+cond,+followed+by+filtration+by+(id,+name)
++++model.all.map+do+%7Cx%7C
++++++cond.(+x+)+?+{+x.id+=>+x.name+}+:+{}
++++end.reduce+Hash.new+do+%7Cmemo,+e%7C+memo.merge(+e+)+end
++end|code-block|syntax|javascript|1632047|在like之后，您可以像这样调用此函数：|1632048|@contests+=+make_select_list+Contest+do+%7Ccontest%7C
++logged_admin?+or+contest.organizer+==+@current_user
end|1632049|如果您不需要过滤您的选择，您只需省略该块：|1632050|@categories+=+make_select_list(+Category+)+#+selects+all+categories|1632051|Ruby代码块的威力就到此为止。|1632052|entityMap|0|LINK|mutability|MUTABLE|url|http://eli.thegreenplace.net/2006/04/18/understanding-ruby-blocks-procs-and-methods/^0|N|C|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|10|8|@]|9|@$A|11|B|12|1|13]]|C|$]]|$1|D|3|E|5|F|7|14|8|@]|9|@]|C|$G|H]]|$1|I|3|J|5|6|7|15|8|@]|9|@]|C|$]]|$1|K|3|L|5|F|7|16|8|@]|9|@]|C|$G|H]]|$1|M|3|N|5|6|7|17|8|@]|9|@]|C|$]]|$1|O|3|P|5|F|7|18|8|@]|9|@]|C|$G|H]]|$1|Q|3|R|5|6|7|19|8|@]|9|@]|C|$]]|$1|S|3|-4|5|6|7|1A|8|@]|9|@]|C|$]]]|T|$U|$5|V|W|X|C|$Y|Z]]]]

I would recommend to use ampersand to have an access to named blocks within a function. Following the recommendations given in <a href="http://eli.thegreenplace.net/2006/04/18/understanding-ruby-blocks-procs-and-methods/" rel="nofollow">this article</a> you can write something like this (this is a real scrap from my working program):

<pre><code> # Returns a valid hash for html form select element, combined of all entities
 # for the given +model+, where only id and name attributes are taken as
 # values and keys correspondingly. Provide block returning boolean if you
 # need to select only specific entities.
 #
 # * *Args* :
 # - +model+ -&gt; ORM interface for specific entities'
 # - +&amp;cond+ -&gt; block {|x| boolean}, filtering entities upon iterations
 # * *Returns* :
 # - hash of {entity.id =&gt; entity.name}
 #
 def make_select_list( model, &amp;cond )
 cond ||= proc { true } # cond defaults to proc { true }
 # Entities filtered by cond, followed by filtration by (id, name)
 model.all.map do |x|
 cond.( x ) ? { x.id =&gt; x.name } : {}
 end.reduce Hash.new do |memo, e| memo.merge( e ) end
 end
</code></pre>

Afterwerds, you can call this function like this:

<pre><code>@contests = make_select_list Contest do |contest|
 logged_admin? or contest.organizer == @current_user
end
</code></pre>

If you don't need to filter your selection, you simply omit the block:

<pre><code>@categories = make_select_list( Category ) # selects all categories
</code></pre>

So much for the power of Ruby blocks.

blocks|key|1417353|text|您也可以使用"+eval+"，并将该方法作为字符串参数传递，然后在另一个方法中简单地对其求值。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1417354|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

you also can use "eval", and pass the method as a string argument, and then simply eval it in the other method.

blocks|key|1417405|text|与Proc或method+call类似，您也可以将lambda作为weightf参数传递：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1417406|def+main
++gaussian+=+->+(params)+{
++++...
++}
++weightedknn(data,+vec1,+k+=+5,+gaussian,+params)
++#+Use+symbol+:gaussian+if+method+exists+instead
end|code-block|syntax|javascript|1417407|def+weightedknn(data,+vec1,+k+=+5,+weightf,+params)
++...
++weight+=+weightf.call(params)
++...
end|1417408|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/a/522771/9527665|1|https://stackoverflow.com/a/523996/9527665^0|X|7|1|4|0|6|B|1|0|0|0^^$0|@$1|2|3|4|5|6|7|W|8|@$9|X|A|Y|B|C]]|D|@$9|Z|A|10|1|11]|$9|12|A|13|1|14]]|E|$]]|$1|F|3|G|5|H|7|15|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|H|7|16|8|@]|D|@]|E|$I|J]]|$1|M|3|-4|5|6|7|17|8|@]|D|@]|E|$]]]|N|$O|$5|P|Q|R|E|$S|T]]|U|$5|P|Q|R|E|$S|V]]]]

Similarly to a <a href="https://stackoverflow.com/a/522771/9527665">Proc</a> or a <a href="https://stackoverflow.com/a/523996/9527665">method call</a>, you can also pass a lambda as <code>weightf</code> parameter :
<pre><code>def main
 gaussian = -&gt; (params) {
 ...
 }
 weightedknn(data, vec1, k = 5, gaussian, params)
 # Use symbol :gaussian if method exists instead
end

</code></pre>
<pre><code>def weightedknn(data, vec1, k = 5, weightf, params)
 ...
 weight = weightf.call(params)
 ...
end
</code></pre>

I am trying to mess around a little bit with Ruby. Therefor I try to implement the algorithms (given in Python) from the book "Programming Collective Intelligence" Ruby.

In chapter 8 the author passes a method a as parameter. This seems to work in Python but not in Ruby.

I have here the method

<pre><code>def gaussian(dist, sigma=10.0)
 foo
end
</code></pre>

and want to call this with another method

<pre><code>def weightedknn(data, vec1, k = 5, weightf = gaussian)
 foo
 weight = weightf(dist)
 foo
end
</code></pre>

All I got is an error

<pre><code>ArgumentError: wrong number of arguments (0 for 1)
</code></pre>

Passing a method as a parameter in Ruby

我正试着和Ruby打成一片。因此，我尝试实现“编程集体智能”Ruby一书中的算法(在Python中给出)。在第八章中，作者传递了一个方法a作为参数。这似乎适用于Python，但不适用于Ruby。我这里有一个方法def gaussian(dist, sigma=10.0)  fooend并希望使用另一个方法调用此方法de...

问在Ruby中将方法作为参数传递
EN

社区

活动

资源

关于

腾讯云开发者

热门产品

热门推荐

更多推荐

问在Ruby中将方法作为参数传递EN

社区

活动

资源

关于

腾讯云开发者

热门产品

热门推荐

更多推荐

问在Ruby中将方法作为参数传递
EN