[英]select a sublist from a list of lists in python
I've got a list of lists A
: 我有一个列表
A
的列表:
A = [ [0, 42, 2.6],
[1, 20, 5.6],
[2, 67, 3.5],
[3, 12, 3.2],
[4, 34, 1.1],
[5, 74, 4.7],
[6, 29, 2.9] ]
from which I'd like to extract a sub-list B
containing only those lists whose second columns are lower than 30 (ie, B = [[1, 20, 5.6],[3, 12, 3.2],[6, 29, 2.9]]
) 我想从中提取一个子列表
B
,该子列表B
仅包含第二列小于30的那些列表(即B = [[1, 20, 5.6],[3, 12, 3.2],[6, 29, 2.9]]
)
Of course I may convert it to a numpy
and use a np.where
. 当然,我可以将其转换为
numpy
并使用np.where
。 However I was wondering whether there is a way of doing that just by using lists. 但是我想知道是否只有通过使用列表才能做到这一点。 I tried with a list comprehension, but I'm not very expert on that:
我尝试了列表理解,但是在这方面我不是很熟练:
B = [x for x in len(A) if x[1] <= 30]
but it doesn't work, indeed. 但这确实不起作用。 Any suggestion?
有什么建议吗? Thanks in advance.
提前致谢。
尝试这个:
B = [x for x in A if x[1] <= 30]
Your current code is attempting to generate an value to be used as an index at each iteration. 您当前的代码正在尝试生成一个值,该值将在每次迭代时用作索引。 To implement that approach, access each row of
A
with x
: 要实现该方法,请使用
x
访问A
每一行:
B = [A[x] for x in range(len(A)) if A[x][1] <= 30]
Note, however, that is much simpler to use a list comprehension or the more functional filter
: 但是请注意,使用列表推导或更实用的
filter
要简单得多:
List comprehension: 清单理解:
B = [i for i in A if i[1] <= 30]
filter
: filter
:
B = list(filter(lambda x:x[1] <= 30, A))
Here is a vectorised approach: 这是一种向量化方法:
import numpy as np
A = np.array([[0, 42, 2.6],
[1, 20, 5.6],
[2, 67, 3.5],
[3, 12, 3.2],
[4, 34, 1.1],
[5, 74, 4.7],
[6, 29, 2.9]])
A[A[:, 1] <= 30]
# array([[ 1. , 20. , 5.6],
# [ 3. , 12. , 3.2],
# [ 6. , 29. , 2.9]])
声明:本站的技术帖子网页,遵循CC BY-SA 4.0协议,如果您需要转载,请注明本站网址或者原文地址。任何问题请咨询:yoyou2525@163.com.