F#:迭代字典只返回自己? [英] F#: Iterating over a dictionary just returns itself?
问题描述
let h = dict [(1,2),(3,4)]
Console.WriteLine(h.Count)
Console.WriteLine(i)
给我
1
[(1,2),(3,4)]
两个问题。首先,为什么迭代一个字典给我一个只有1个项目的序列,dict本身?这可能有一些逻辑,也将影响我最终尝试迭代的其他事情。对于由any(),All(),Aggregate()等暴露的所有其他Seq成员,这意味着什么)?
其次,是否有很好的迭代方式,通常会在字典中操作键值对,就像Python一样?
您使用逗号分配分号。
[(1,2); (3,4)]
元组的逗号,列表元素的分号。 (这里的括号是可选的。)
如果要迭代字典中的键值对,可以使用
$ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $
使用 KeyValue 活动模式。
let h = dict [(1, 2), (3, 4)]
Console.WriteLine(h.Count)
for i in h do
Console.WriteLine(i)
gives me
1
[(1, 2), (3, 4)]
Two questions. Firstly, why does iterating over a dict give me back a sequence which only has 1 item, the dict itself? There is probably some logic behind this that will also affect other things I end up trying to iterate over. What does this mean for all the other Seq members exposed by dict (Any(), All(), Aggregate(), etc.)?
Secondly, is there a good way to iterate over and generally manipulate the key-value pairs in the dictionary, like in Python?
You used a comma where you need a semicolon.
[(1,2); (3,4)]
Commas for tuples, semicolons for list elements. (The parens here are optional.)
If you want to iterate over key-value pairs in the dictionary, you can use
for KeyValue(k,v) in someDictionary do ...
which uses the KeyValue active pattern.
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