[英]Linq ToList/ToArray/ToDictionary performance
Well I encounter many situations where having an IEnumerable is not enough. 好吧,我遇到很多情况,IEnumerable是不够的。 However I'm unsure about the performance of the above method calls.
但是我不确定上述方法调用的性能。
What I really want to ask is: 我真正想问的是:
Is the performance of ToList/ToArray: 是ToList / ToArray的性能:
If I called a linq extention method on a list, it has an O(1) performance if I call ToList but O(n) if call ToArray (and the opposite if my original list was an array) ? 如果我在列表上调用linq扩展方法,如果我调用ToList则它具有O(1)性能,如果调用ToArray则具有O(n)(如果我的原始列表是数组则相反)?
Some magic happens and the performance is O(1)? 一些魔法发生了,性能是O(1)?
Probably to Dictionary is O(n), right ? 字典可能是O(n),对吧?
Is the performance of
ToList
/ToArray
an O(n) operation which copies theIEnumerable
to a new array/List ?ToList
/ToArray
的性能是否是将IEnumerable
复制到新数组/列表的O(n)操作?
Yes. 是。
ToList
is slightly more efficient, as it doesn't need to trim the internal buffer to the right length first. ToList
稍微高效一些,因为它不需要先将内部缓冲区修剪到合适的长度。
If I called a linq extention method on a list, it has an O(1) performance if I call ToList but O(n) if call ToArray (and the opposite if my original list was an array) ?
如果我在列表上调用linq扩展方法,如果我调用ToList则它具有O(1)性能,如果调用ToArray则具有O(n)(如果我的原始列表是数组则相反)?
No. For both calls, a new collection is always created; 不会。对于这两个电话,总会创建一个新的集合; that's a shallow copy of the original collection.
这是原始集合的浅层副本。 It's more efficient to call
ToList
or ToArray
on any ICollection<T>
than on a simple IEnumerable<T>
which doesn't implement ICollection<T>
though, as with a collection the length is known to start with. 在任何
ICollection<T>
上调用ToList
或ToArray
比在没有实现ICollection<T>
的简单IEnumerable<T>
上调用更有效,就像已知长度的集合一样。 (This is detected at execution time though; you don't need to worry about the compile-time type.) (这在执行时检测到;您不必担心编译时类型。)
Probably to Dictionary is O(n), right ?
字典可能是O(n),对吧?
Assuming the hash is sensible, it's O(N), yes. 假设散列是合理的,那就是O(N),是的。 Basically it creates a new dictionary in exactly the way you'd probably expect it to.
基本上它会以您可能期望的方式创建一个新的字典。
You might want to read the corresponding posts in my Edulinq blog series: 您可能想阅读我的Edulinq博客系列中的相应帖子:
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