Python 如何按列对多维数组进行排序？
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How to sort multidimensional array by column?
提问by Web Hopeful
Is there a way to use the sort() method or any other method to sort a list by column? Lets say I have the list:
有没有办法使用 sort() 方法或任何其他方法按列对列表进行排序？假设我有清单：
[
[John,2],
[Jim,9],
[Jason,1]
]
And I wanted to sort it so that it would look like this:
我想对其进行排序，使其看起来像这样：
[
[Jason,1],
[John,2],
[Jim,9],
]
What would be the best approach to do this?
这样做的最佳方法是什么？
Edit:
编辑：
Right now I am running into an index out of range error. I have a 2 dimensional array that is lets say 1000 rows b 3 columns. I want to sort it based on the third column. Is this the right code for that?
现在我遇到了索引超出范围的错误。我有一个二维数组，可以说 1000 行 b 3 列。我想根据第三列对其进行排序。这是正确的代码吗？
sorted_list = sorted(list_not_sorted, key=lambda x:x[2])
采纳答案by roippi
Yes. The sortedbuilt-in accepts a keyargument:
是的。该sorted内置接受key的说法：
sorted(li,key=lambda x: x[1])
Out[31]: [['Jason', 1], ['John', 2], ['Jim', 9]]
note that sortedreturns a new list. If you want to sort in-place, use the .sortmethod of your list (which also, conveniently, accepts a keyargument).
请注意，sorted返回一个新列表。如果您想就地排序，请使用.sort列表的方法（它也方便地接受一个key参数）。
or alternatively,
或者，
from operator import itemgetter
sorted(li,key=itemgetter(1))
Out[33]: [['Jason', 1], ['John', 2], ['Jim', 9]]
回答by squiguy
You can use the sorted method with a key.
您可以使用带有键的 sorted 方法。
sorted(a, key=lambda x : x[1])
回答by roippi
You can use list.sortwith its optional keyparameterand a lambdaexpression:
您可以使用list.sort其可选key参数和lambda表达式：
>>> lst = [
... ['John',2],
... ['Jim',9],
... ['Jason',1]
... ]
>>> lst.sort(key=lambda x:x[1])
>>> lst
[['Jason', 1], ['John', 2], ['Jim', 9]]
>>>
This will sort the list in-place.
这将就地对列表进行排序。
Note that for large lists, it will be faster to use operator.itemgetterinstead of a lambda:
请注意，对于大型列表，使用operator.itemgetter代替 a会更快lambda：
>>> from operator import itemgetter
>>> lst = [
... ['John',2],
... ['Jim',9],
... ['Jason',1]
... ]
>>> lst.sort(key=itemgetter(1))
>>> lst
[['Jason', 1], ['John', 2], ['Jim', 9]]
>>>
回答by John La Rooy
The optional keyparameter to sort/sortedis a function. The function is called for each item and the return values determine the ordering of the sort
/的可选key参数是一个函数。为每个项目调用该函数，返回值确定排序的顺序sortsorted
>>> lst = [['John', 2], ['Jim', 9], ['Jason', 1]]
>>> def my_key_func(item):
... print("The key for {} is {}".format(item, item[1]))
... return item[1]
...
>>> sorted(lst, key=my_key_func)
The key for ['John', 2] is 2
The key for ['Jim', 9] is 9
The key for ['Jason', 1] is 1
[['Jason', 1], ['John', 2], ['Jim', 9]]
taking the printout of the function leaves
取print出来的功能叶
>>> def my_key_func(item):
... return item[1]
This function is simple enough to write "inline" as a lambda function
这个函数很简单，可以将“内联”写成一个 lambda 函数
>>> sorted(lst, key=lambda item: item[1])
[['Jason', 1], ['John', 2], ['Jim', 9]]
回答by kevin
sorted(list, key=lambda x: x[1])
Note: this works on time variable too.
注意：这也适用于时间变量。
