[英]Making a new list with tuples based on strings in the list
L = ["5", "0 1", "0 2", "1 3", "2 3", "2 4", "3 4"]
Each number represents a person. 每个数字代表一个人。 So, there are five people from 0 to 4 in the list.
因此,列表中有5个人,从0到4。
L[0]
always shows how many people are in the list. L[0]
始终显示列表中有多少人。
L1 = [(0,[1,2]), (1, [3]), (2, [3,4]), (3, [4])]
The person "0"
is paired with 1
and 2
. 人
"0"
与1
和2
配对。 So, it has a list of 1, 2
in a tuple. 因此,它在一个元组中具有
1, 2
的列表。 My approach to get the result above is to compare the first character in L[1]
to the end of the list. 我获得以上结果的方法是将
L[1]
的第一个字符与列表的末尾进行比较。 If the first letter in L[1]
matches with the first letter in L[2]
, it bundles the second letter in L[2]
with the second letter in L[1]
. 如果
L[1]
中的第一个字母与L[2]
的第一个字母匹配,则会将L[2]
中的第二个字母与L[1]
的第二个字母捆绑在一起。 Finally, the new list is paired with 0
in a tuple. 最后,新列表在元组中与
0
配对。 By the way, I cannot come up with such thing that can check the first letter in strings. 顺便说一句,我无法提出可以检查字符串中第一个字母的东西。 I am not sure if this approach is right or not.
我不确定这种方法是否正确。
I am struggling to make such list L1
above. 我努力在上面列出这样的清单
L1
。 Could anyone let me know if my approach to this question is right? 谁能告诉我我对这个问题的解决方法是否正确? If it is wrong, please briefly give me a hint to solve this.
如果有误,请简要提示我解决此问题。
Using list comprehension 使用列表理解
Created a list in the required range, considering L[0]
考虑到
L[0]
,在所需范围内创建了一个列表
Checks for matches between the element and the other items using startswith
使用
startswith
检查元素和其他项目之间的匹配
L = ["5", "0 1", "0 2", "1 3", "2 3", "2 4", "3 4"]
L1 = [(0,[1,2]), (1, [3]), (2, [3,4]), (3, [4])] # required list
L2 = [ (i, [ int(x[-1]) for x in L if str(x).startswith(str(i)) ]) for i in range(int(L[0])-1) ]
Output 产量
[(0, [1, 2]), (1, [3]), (2, [3, 4]), (3, [4])]
[(0, [1, 2]), (1, [3]), (2, [3, 4]), (3, [4])]
Probably the best thing is to first use a defaultdict
: 最好的办法是先使用
defaultdict
:
from collections import defaultdict
from itertools import islice
result = defaultdict(list)
for li in islice(L,1,None):
h, *others = map(int,li.split())
for other in others:
result[h].append(other)
Or a version that works for python-2.x : 或适用于python-2.x的版本 :
from collections import defaultdict
from itertools import islice
result = defaultdict(list)
for li in islice(L,1,None):
data = map(int,li.split())
h = data[0]
for other in data[1:]:
result[h].append(other)
and then we obtain the items
of that dictionary: 然后我们获得该词典的
items
:
L1 = list(result.items())
This produces: 这将产生:
>>> L1
[(0, [1, 2]), (1, [3]), (2, [3, 4]), (3, [4])]
Note that in this case the items are not ordered: since a dictionary in Python usually has no order (the latest implementations in CPython have, but this is seen as an implementation detail). 请注意,在这种情况下,项目没有顺序:因为Python中的字典通常没有顺序(CPython中的最新实现是有顺序的,但这被视为实现细节)。
But converting the dictionary back into a list is not logical, since the advantage of a dictionary is a fast lookup (in O(1) , constant time). 但是将字典转换回列表是不合逻辑的,因为字典的优点是可以快速查找(在O(1)中为常数时间)。
We can make the last part more elegant by writing: 我们可以通过编写以下内容使最后一部分更优雅:
from collections import defaultdict
result = defaultdict(list)
for li in islice(L,1,None):
h, *others = map(int,li.split())
result[h] += others
Instead of list, go with dict and use this pattern without importing any external module. 而不是列表,请使用dict并使用此模式,而无需导入任何外部模块。
L = ["5", "0 1", "0 2", "1 3", "2 3", "2 4", "3 4"]
final_dict={}
new=[]
for item in L:
if not len(item)<2:
if int(item[0]) not in final_dict:
final_dict[int(item[0])]=[int(item[2])]
else:
final_dict[int(item[0])].append(int(item[2]))
print(final_dict)
output: 输出:
{0: [1, 2], 1: [3], 2: [3, 4], 3: [4]}
or if you want the result in the list then add this line end of above code: 或者,如果您希望结果在列表中,则在上面的代码中添加以下行:
print([(key,value) for key,value in final_dict.items()])
output: 输出:
[(0, [1, 2]), (1, [3]), (2, [3, 4]), (3, [4])]
I would suggest you use a form of dictionary
for easier processing of the data later on. 我建议您使用
dictionary
的形式,以便以后更轻松地处理数据。 So here, defualtdict
would be best utilized. 因此,这里最好使用
defualtdict
。
>>> from collections import defaultdict
>>> L = ["5", "0 1", "0 2", "1 3", "2 3", "2 4", "3 4"]
>>> n = int(L.pop(0)) #number of people
>>> d = defaultdict(list)
>>> for ele in L:
x, y = map(int, ele.split())
d[x].append(y)
>>> d
=> defaultdict(<class 'list'>, {0: [1, 2], 1: [3], 2: [3, 4], 3: [4]})
If neccessary to have that list
format, use dict.items()
and type cast it to list
如果需要具有该
list
格式,请使用dict.items()
并键入将其dict.items()
为list
>>> l1 = list(d.items())
>>> l1
=> [(0, [1, 2]), (1, [3]), (2, [3, 4]), (3, [4])]
Here is an itertools.groupy
solution. 这是一个
itertools.groupy
解决方案。 (The commented out line also considers reverse pairs.) (注释行还考虑反向对。)
import itertools as it
import operator as op
def L1(L):
# split pairs
L = [p.split() for p in L[1:]]
# convert to int
L = [(int(P1), int(P2)) for P1, P2 in L]
LL = sorted(L)
# # add reversed and sort
# LL = sorted(L + [P[::-1] for P in L])
# group by first element
res = it.groupby(LL, op.itemgetter(0))
# make proper lists
return [(k, [P[1] for P in v]) for k, v in res]
Output (for the example L
): 输出(例如
L
):
[(0, [1, 2]), (1, [3]), (2, [3, 4]), (3, [4])]
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