entityMap|0|type|LINK|mutability|MUTABLE|data|url|https://docs.python.org/3/library/itertools.html#itertools.groupby|blocks|key|fd0op|text|有(差不多？)没有itertools做不到的事情。看一看groupby|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|16gvt|from+itertools+import+groupby
from+operator+import+attrgetter


class+Element:
++++def+__init__(self,+id,+value):
++++++++self.id+=+id
++++++++self.value+=+value
++++def+__repr__(self):++#+kudos+@mesejo
++++++++return+"Element({},+{})".format(self.id,+self.value)

l+=+[Element(1,+100),+Element(1,+200),+Element(2,+1),+Element(3,+4),+Element(3,+4)]

l.sort(key=attrgetter('id'))++#+if+it+is+already+sorted+by+'id',+comment-out

res+=+[Element(g,+sum(sub.value+for+sub+in+k))+for+g,+k+in+groupby(l,+key=attrgetter('id'))]|code-block|syntax|javascript|3dh1r|这会导致：|5tlj4|print(res)+++#+[Element(1,+300),+Element(2,+1),+Element(3,+8)]|bp699^0|9|9|S|7|S|7|0|0|0|0|0^^$0|$1|$2|3|4|5|6|$7|8]]]|9|@$A|B|C|D|2|E|F|W|G|@$H|X|I|Y|J|K]|$H|Z|I|10|J|K]]|L|@$H|11|I|12|A|13]]|6|$]]|$A|M|C|N|2|O|F|14|G|@]|L|@]|6|$P|Q]]|$A|R|C|S|2|E|F|15|G|@]|L|@]|6|$]]|$A|T|C|U|2|O|F|16|G|@]|L|@]|6|$P|Q]]|$A|V|C|-4|2|E|F|17|G|@]|L|@]|6|$]]]]

There is (almost?) nothing that <code>itertools</code> cannot do. Take a look at <a href="https://docs.python.org/3/library/itertools.html#itertools.groupby" rel="nofollow noreferrer"><code>groupby</code></a>:

<pre><code>from itertools import groupby
from operator import attrgetter


class Element:
 def __init__(self, id, value):
 self.id = id
 self.value = value
 def __repr__(self): # kudos @mesejo
 return "Element({}, {})".format(self.id, self.value)

l = [Element(1, 100), Element(1, 200), Element(2, 1), Element(3, 4), Element(3, 4)]

l.sort(key=attrgetter('id')) # if it is already sorted by 'id', comment-out

res = [Element(g, sum(sub.value for sub in k)) for g, k in groupby(l, key=attrgetter('id'))]
</code></pre>

which results in:

<pre><code>print(res) # [Element(1, 300), Element(2, 1), Element(3, 8)]
</code></pre>

entityMap|0|type|LINK|mutability|MUTABLE|data|url|https://docs.python.org/3/library/collections.html#collections.defaultdict|1|https://docs.python.org/3/library/itertools.html#itertools.starmap|blocks|key|e12tp|text|一种方法是创建一个将ids映射到值和的defaultdict。然后我们可以利用这些结果并使用它们来构建一个新的Elements列表。为此，一种方法是使用starmap将该字典中的条目映射到Element的参数|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|36hcb|from+collections+import+defaultdict
from+itertools+import+starmap

class+Element:
++++def+__init__(self,+id,+value):
++++++++self.id+=+id
++++++++self.value+=+value
++++def+__repr__(self):
++++++++return+"Element({},+{})".format(self.id,+self.value)

l+=+[Element(1,+100),+Element(1,+200),+Element(2,+1),+Element(3,+4),+Element(3,+4)]

d+=+defaultdict(int)

for+e+in+l:
++++d[e.id]+%2B=+e.value

print(list(starmap(Element,+d.items())))
#+[Element(1,+300),+Element(2,+1),+Element(3,+8)]|code-block|syntax|javascript|elrkg^0|J|B|1J|8|24|7|2M|7|J|B|0|24|7|1|0|0^^$0|$1|$2|3|4|5|6|$7|8]]|9|$2|3|4|5|6|$7|A]]]|B|@$C|D|E|F|2|G|H|U|I|@$J|V|K|W|L|M]|$J|X|K|Y|L|M]|$J|Z|K|10|L|M]|$J|11|K|12|L|M]]|N|@$J|13|K|14|C|15]|$J|16|K|17|C|18]]|6|$]]|$C|O|E|P|2|Q|H|19|I|@]|N|@]|6|$R|S]]|$C|T|E|-4|2|G|H|1A|I|@]|N|@]|6|$]]]]

One way would be to create a <a href="https://docs.python.org/3/library/collections.html#collections.defaultdict" rel="nofollow noreferrer"><code>defaultdict</code></a> that maps ids to sums of values. Then we can take those results and use them to build a new list of <code>Elements</code>. One way to do that is to use <a href="https://docs.python.org/3/library/itertools.html#itertools.starmap" rel="nofollow noreferrer"><code>starmap</code></a> to map the items of that dictionary to the arguments to <code>Element</code>

<pre><code>from collections import defaultdict
from itertools import starmap

class Element:
 def __init__(self, id, value):
 self.id = id
 self.value = value
 def __repr__(self):
 return "Element({}, {})".format(self.id, self.value)

l = [Element(1, 100), Element(1, 200), Element(2, 1), Element(3, 4), Element(3, 4)]

d = defaultdict(int)

for e in l:
 d[e.id] += e.value

print(list(starmap(Element, d.items())))
# [Element(1, 300), Element(2, 1), Element(3, 8)]
</code></pre>

entityMap|blocks|key|1nbmi|text|您还可以使用set来获取惟一的ids，使用sum来合计值，从而获得所需的结果。例如：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|11nj1|class+Element:
++++def+__init__(self,+id,+value):
++++++++self.id+=+id
++++++++self.value+=+value

l+=+[Element(1,+100),+Element(1,+200),+Element(2,+1),+Element(3,+4),+Element(3,+4)]

ids+=+set(elem.id+for+elem+in+l)
totals+=+[Element(i,+sum(elem.value+for+elem+in+l+if+elem.id+==+i))+for+i+in+ids]
#+[Element(1,+300),+Element(2,+1),+Element(3,+8)]|code-block|syntax|javascript|bid15^0|6|3|L|3|0|0^^$0|$]|1|@$2|3|4|5|6|7|8|M|9|@$A|N|B|O|C|D]|$A|P|B|Q|C|D]]|E|@]|F|$]]|$2|G|4|H|6|I|8|R|9|@]|E|@]|F|$J|K]]|$2|L|4|-4|6|7|8|S|9|@]|E|@]|F|$]]]]

You could also get the desired result using <code>set</code> to get just the unique ids and <code>sum</code> to total the values. For example:

<pre><code>class Element:
 def __init__(self, id, value):
 self.id = id
 self.value = value

l = [Element(1, 100), Element(1, 200), Element(2, 1), Element(3, 4), Element(3, 4)]

ids = set(elem.id for elem in l)
totals = [Element(i, sum(elem.value for elem in l if elem.id == i)) for i in ids]
# [Element(1, 300), Element(2, 1), Element(3, 8)]
</code></pre>

I have a python list <code>l</code> containing instances of the class <code>Element</code>:



<pre class="lang-py prettyprint-override"><code>class Element:
 def __init__(self, id, value):
 self.id = id
 self.value = value

l = [Element(1, 100), Element(1, 200), Element(2, 1), Element(3, 4), Element(3, 4)]
</code></pre>

Now I want to sum all <code>value</code> members of the classes <code>Elements</code> if their <code>id</code> is equal to obtain this list:

<pre class="lang-py prettyprint-override"><code>l = [Element(1, 300), Element(2, 1), Element(3, 8)]
</code></pre>

What is the most pythonic way to do this?

Sum of values in list when condition is met

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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 我有一个包含类Element实例的python列表l class Element:    def __init__(self, id, value):        self.id = id        self.value = valuel = [Element(1, 100), Element(1, 200),...

问满足条件时列表中的值之和
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问满足条件时列表中的值之和EN