blocks|key|384603|text|您可以使用包含双精度值的temp变量创建一个新的字典-这利用了这样一个事实，即枚举和添加字典是逐项完成的，因此temp包含正确的双精度值：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|384604|double+temp+=+0;
var+numDict+=+myDictionary.Where(kvp+=>+Double.TryParse(kvp.Value,+out+temp))
++++++++++++++++++++++++++.ToDictionary(+x=>+x.Key,+x=>+temp);|code-block|syntax|javascript|384605|entityMap^0|C|4|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 just create a new dictionary using the <code>temp</code> variable which contains the double value - this exploits the fact that the enumeration and addition to the dictionary is done item by item so temp contains the correct double value:

<pre><code>double temp = 0;
var numDict = myDictionary.Where(kvp =&gt; Double.TryParse(kvp.Value, out temp))
 .ToDictionary( x=&gt; x.Key, x=&gt; temp);
</code></pre>

blocks|key|4423758|text|您给出的代码不仅难看，而且在执行时会出现InvalidCastException错误。我怀疑你真的想：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|4423759|var+numericData+=+myDictionary
++++++++.Select(kvp+=>+{
++++++++++++++++++++double+value;
++++++++++++++++++++return+new+{+kvp.Key,
++++++++++++++++++++++++Value+=+double.TryParse(kvp.Value,+out+value)+
+++++++++++++++++++++++++++++++++++?+value+:+(double?)+null
++++++++++++++++++++};
+++++++++++++++})
++++++++.Where(pair+=>+pair.Value+!=+null)
++++++++.ToDictionary(pair+=>+pair.Key,+pair+=>+pair.Value.Value);|code-block|syntax|javascript|4423760|是的，这是丑陋的--但是：|4423761|4423762|它避免了多次解析该值|unordered-list-item|4423763|它避免了将副作用放入查询|4423764|中|4423765|如果你乐于解析两次，你可以让它稍微更干净一些，但效率会更低：|4423766|var+numericData+=+myDictionary
+++++++.Where(kvp+=>+{+double+tmp;+return+double.TryParse(kvp.Value,+out+tmp);+})
+++++++.ToDictionary(pair+=>+pair.Key,+pair+=>+double.Parse(pair.Value));|4423767|或者(更简洁地)，您可以创建一个单独的方法：|4423768|public+static+double?+TryParseNullableDouble(string+text)
{
++++double+value;
++++return+double.TryParse(text,+out+value)+?+value+:+(double?)+null;
}|4423769|然后第一个版本变成：|4423770|var+numericData+=+myDictionary
++++++++.Select(kvp+=>+new+{+kvp.Key,+TryParseNullableDouble(kvp.Value)+})
++++++++.Where(pair+=>+pair.Value+!=+null)
++++++++.ToDictionary(pair+=>+pair.Key,+pair+=>+pair.Value.Value);|4423771|entityMap^0|K|K|0|0|0|0|0|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|18|8|@$9|19|A|1A|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|1B|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|1C|8|@]|D|@]|E|$]]|$1|M|3|-4|5|6|7|1D|8|@]|D|@]|E|$]]|$1|N|3|O|5|P|7|1E|8|@]|D|@]|E|$]]|$1|Q|3|R|5|P|7|1F|8|@]|D|@]|E|$]]|$1|S|3|T|5|6|7|1G|8|@]|D|@]|E|$]]|$1|U|3|V|5|6|7|1H|8|@]|D|@]|E|$]]|$1|W|3|X|5|H|7|1I|8|@]|D|@]|E|$I|J]]|$1|Y|3|Z|5|6|7|1J|8|@]|D|@]|E|$]]|$1|10|3|11|5|H|7|1K|8|@]|D|@]|E|$I|J]]|$1|12|3|13|5|6|7|1L|8|@]|D|@]|E|$]]|$1|14|3|15|5|H|7|1M|8|@]|D|@]|E|$I|J]]|$1|16|3|-4|5|6|7|1N|8|@]|D|@]|E|$]]]|17|$]]

The code you've given is not only ugly - it will fail with an <code>InvalidCastException</code> at execution time. I suspect you actually want:

<pre><code>var numericData = myDictionary
 .Select(kvp =&gt; {
 double value;
 return new { kvp.Key,
 Value = double.TryParse(kvp.Value, out value) 
 ? value : (double?) null
 };
 })
 .Where(pair =&gt; pair.Value != null)
 .ToDictionary(pair =&gt; pair.Key, pair =&gt; pair.Value.Value);
</code></pre>

And yes, that's ugly - but:

<ul>
<li>It avoids parsing the value more than once</li>
<li>It avoids putting side-effects in your query</li>
</ul>

You can make it slightly cleaner but less efficient if you're happy to parse twice:

<pre><code>var numericData = myDictionary
 .Where(kvp =&gt; { double tmp; return double.TryParse(kvp.Value, out tmp); })
 .ToDictionary(pair =&gt; pair.Key, pair =&gt; double.Parse(pair.Value));
</code></pre>

Or (more cleanly) you could create a separate method:

<pre><code>public static double? TryParseNullableDouble(string text)
{
 double value;
 return double.TryParse(text, out value) ? value : (double?) null;
}
</code></pre>

Then the first version becomes:

<pre><code>var numericData = myDictionary
 .Select(kvp =&gt; new { kvp.Key, TryParseNullableDouble(kvp.Value) })
 .Where(pair =&gt; pair.Value != null)
 .ToDictionary(pair =&gt; pair.Key, pair =&gt; pair.Value.Value);
</code></pre>

I have a generic Dictionary where TValue is of type <code>String</code> (<code>Dictionary&lt;int, string&gt;</code>). I chose to use string as the value type because the data was loaded from an Xml file where the source values can be character or numeric data types (I suppose <code>Object</code> would've been an acceptable TValue type too, but even then this question would be equally applicable). 

The character data types also have importance, so excluding them outright isn't an option.

I'd like to extract a subset of this <code>Dictionary&lt;int, double&gt;</code>. In other words, I'd like the subset of the dictionary where the values are numeric. 

Right now I'm doing it like this: 

<pre><code>Dictionary&lt;int, string&gt; myDictionary;
// Do some loading.
var numericData = myDictionary.Where(kvp =&gt; Double.TryParse(kvp.Value, out temp) 
</code></pre>

This approach is awfully ugly and doesn't get me the result as a <code>Dictionary&lt;int, double&gt;</code> Can anyone offer other ways to improve this?

Thanks!

Extracting a Dictionary<TKey, double> from a Dictionary<TKey, string> instance

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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我有一个通用字典，其中TValue的类型是String (Dictionary<int, string>)。我选择使用字符串作为值类型，因为数据是从一个Xml文件加载的，该文件的源值可以是字符或数字数据类型(我认为Object也是一种可以接受的TValue类型，但即使这样，这个问题也同样适用)。字符数据类型也很重要，所...

问从Dictionary<TKey，string>实例中提取Dictionary<TKey，double>
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