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This question already has answers here:
How do I compute all possibilities for an array of numbers/bits (in python, or any language for that matter)
(5 answers)
Closed 2 years ago.
I am trying to achieve the following. I have a 2D array, which is of a 4x4 dimension. I want to get all possibilities, where I can insert a single 1 instead of a zero, and return an array, which contains all of these possibilities
So if we take:
[[0, 1, 0, 0], [0, 0, 1, 0], [0, 0, 0, 0], [0, 0, 0, 0]]
would result in:
[[1, 1, 0, 0], [0, 0, 1, 0], [0, 0, 0, 0], [0, 0, 0, 0]]
[[0, 1, 1, 0], [0, 0, 1, 0], [0, 0, 0, 0], [0, 0, 0, 0]]
[[0, 1, 0, 1], [0, 0, 1, 0], [0, 0, 0, 0], [0, 0, 0, 0]]
...
There would be a total of 14 entries in the resulting array, since there were 14 zeroes in the input array.
The problem is, that the code I have currently should work, as far as I understand, but I can't seem to get where it goes wrong.
def getPossibilities(arr):
p = []
for i in range(4):
for j in range(4):
if arr[i][j] == 0:
p.append(arr)
p[-1][i][j]=1
return p
for i in getPossibilities([[0,1,0,0],[0,0,1,0],[0,0,0,0],[0,0,0,0]]):
print(i)
This results in 14 arrays of solid ones.
I included the way I check the results, in case there is an error there. I also tried with first copying the arr array into a temporary one, then make the changes, but to no avail.
What goes wrong here? I cannot seem to find an answer. Also, is there a more elegant and faster way of doing this? It would be really beneficial for my usecase.
Thank you very much in advance!
This is somewhat tricky but since you have a list of lists, the copy won't work and you will be changing the array every time, what you need is deepcopy:
import copy
def getPossibilities(arr):
p = []
for i in range(4):
for j in range(4):
if arr[i][j] == 0:
tmp = copy.deepcopy(arr)
tmp[i][j]=1
p.append(tmp)
return p
for i in getPossibilities([[0,1,0,0],[0,0,1,0],[0,0,0,0],[0,0,0,0]]):
print(i)
[[1, 1, 0, 0], [0, 0, 1, 0], [0, 0, 0, 0], [0, 0, 0, 0]]
[[0, 1, 1, 0], [0, 0, 1, 0], [0, 0, 0, 0], [0, 0, 0, 0]]
[[0, 1, 0, 1], [0, 0, 1, 0], [0, 0, 0, 0], [0, 0, 0, 0]]
[[0, 1, 0, 0], [1, 0, 1, 0], [0, 0, 0, 0], [0, 0, 0, 0]]
[[0, 1, 0, 0], [0, 1, 1, 0], [0, 0, 0, 0], [0, 0, 0, 0]]
[[0, 1, 0, 0], [0, 0, 1, 1], [0, 0, 0, 0], [0, 0, 0, 0]]
[[0, 1, 0, 0], [0, 0, 1, 0], [1, 0, 0, 0], [0, 0, 0, 0]]
[[0, 1, 0, 0], [0, 0, 1, 0], [0, 1, 0, 0], [0, 0, 0, 0]]
[[0, 1, 0, 0], [0, 0, 1, 0], [0, 0, 1, 0], [0, 0, 0, 0]]
[[0, 1, 0, 0], [0, 0, 1, 0], [0, 0, 0, 1], [0, 0, 0, 0]]
[[0, 1, 0, 0], [0, 0, 1, 0], [0, 0, 0, 0], [1, 0, 0, 0]]
[[0, 1, 0, 0], [0, 0, 1, 0], [0, 0, 0, 0], [0, 1, 0, 0]]
[[0, 1, 0, 0], [0, 0, 1, 0], [0, 0, 0, 0], [0, 0, 1, 0]]
[[0, 1, 0, 0], [0, 0, 1, 0], [0, 0, 0, 0], [0, 0, 0, 1]]
I want that:
num = 3
array = [0,0,0,0,0]
become this:
array = ([0,0,0,0,0],[0,0,0,0,0],[0,0,0,0,0])
I've tried this:
array = ([0,0,0,0,0],)*num
and this:
array = [[0,0,0,0,0]]*num
but when I set the values, it sets it everywhere.
num = 3
array = [[0,0,0,0,0]]*num
print(array)
array[0][0] = 1
array[1][1] = 2
print(array)
[[0, 0, 0, 0, 0], [0, 0, 0, 0, 0], [0, 0, 0, 0, 0]]
[[1, 2, 0, 0, 0], [1, 2, 0, 0, 0], [1, 2, 0, 0, 0]]
when it should be that:
[[0, 0, 0, 0, 0], [0, 0, 0, 0, 0], [0, 0, 0, 0, 0]]
[[1, 0, 0, 0, 0], [0, 2, 0, 0, 0], [0, 0, 0, 0, 0]]
Use List Comprehensions to build the 2D list . The thing that you are doing is actually making 3(num) references to the same list !! To understand it much better, consider this example
>>> a=b=[5]
>>> a[0] = 6
>>> a
[6]
>>> b
[6]
So use list comprehensions, so that all the inner lists are "unique".
num = 3
array = [[0,0,0,0,0] for i in range(num)]
print(array)
array[0][0] = 1
array[1][1] = 2
print(array)
Output:
[[0, 0, 0, 0, 0], [0, 0, 0, 0, 0], [0, 0, 0, 0, 0]]
[[1, 0, 0, 0, 0], [0, 2, 0, 0, 0], [0, 0, 0, 0, 0]]
This question already has answers here:
List of lists changes reflected across sublists unexpectedly
(17 answers)
Closed 7 years ago.
s is a list of lists of integers with all values initialized to zero. I would like to increment only the first element of the first row by one, but the following command increments the first element of every row by one. How may I achieve this?
In [6]: s = [[0]*4]*4
In [7]: s[0][0] += 1
In [8]: s
Out[8]:
[[1, 0, 0, 0, 0],
[1, 0, 0, 0, 0],
[1, 0, 0, 0, 0],
[1, 0, 0, 0, 0],
[1, 0, 0, 0, 0]]
Okay! Thanks for the advice, the problem was in my construction of s.
If s is truly a list of lists (and not a list containing multiple references to the same list), what you did works, your issue must be elsewhere
>>> s = [[0, 0, 0, 0, 0],
... [0, 0, 0, 0, 0],
... [0, 0, 0, 0, 0],
... [0, 0, 0, 0, 0],
... [0, 0, 0, 0, 0]]
>>> s[0][0]
0
>>> s[0][0] = 1
>>> s
[[1, 0, 0, 0, 0], [0, 0, 0, 0, 0], [0, 0, 0, 0, 0], [0, 0, 0, 0, 0], [0, 0, 0, 0, 0]]
You made your lists "incorrectly" in the first place; each element of your list simply points to the same single list. When you update that list they all update.
Make the list of lists using code something like this instead:
s = [[0 for _ in range(5)] for _ in range(5)]
This is classical Python oversight since lists assignments are done by references not by deep copy.
For example if you constructed using this way that's where it would have gone wrong.
>>> zeros = [0,0,0,0]
>>> s = [zeros,zeros,zeros,zeros]
>>> s[0][0]+=1
>>> s
[[1, 0, 0, 0], [1, 0, 0, 0], [1, 0, 0, 0], [1, 0, 0, 0]]
So while copying lists use as below
>>> s = [list(zeros), list(zeros), list(zeros), list(zeros)]
>>> s[0][0]+=1
>>> s
[[1, 0, 0, 0, 0], [0, 0, 0, 0, 0], [0, 0, 0, 0, 0], [0, 0, 0, 0, 0], [0, 0, 0, 0, 0]]
Hi there i'm having troubles while copying arrays. I know there is really good posts about this but they dont resolve my problems.
First of all Im trying to copy nested arrays so the copy using slice do not work:
new_list = old_list[:]
This does not work when used with nested arrays, and I understand why it doesn't.
For my purposes i need to work with nested arrays so i've been using:
new_list = list(old_list)
This does copy correctly nested arrays but has a strange behavior when used inside a method. Here is an example code:
Edited Code:
def copy_and_reset(data):
import copy
events_data=list(data)
reset_to_0(data)
return events_data
def reset_to_0(the_array):
for i, e in enter code hereenumerate(the_array):
if isinstance(e, list):
reset_to_0(e)
else:
the_array[i] = 0
a=[[1,1,1,1,1],[2,2,2,2,2,2],[3,3,3,3,3,3],[4,4,4,4]]
b=copy_and_reset(a)
print a
print b
b=list(a)
a.append([22,22])
print a
print b
And here is the output:
[[0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0], [0, 0, 0, 0]]
[[0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0], [0, 0, 0, 0]]
[[0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0], [0, 0, 0, 0], [22, 22]]
[[0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0], [0, 0, 0, 0]]
Some idea what happens there? The only way to correctly copy an array inside a method is:
new_list = copy.deepcopy(old_list)
When you are copying the list you are just creating a reference to the lists contained in A. Here is a visualaztion of whats happening:
If you want to step though and view whats happening you should check out PythonTutor
I'm making a water simulation program, and I need it to do a for loop through y, x. But I need it to check the most bottom y first, then up. This is my lvl:
lvl = [[0, 0, 1, 0, 0],
[0, 0, 1, 0, 0],
[0, 0, 1, 0, 0],
[0, 0, 0, 0, 0],
[0, 0, 0, 0, 0]]
I need it to check lvl[4] and then lvl[3], lvl[2], etc. Please help!
NB: I'm using nested for loops, so I can check y, x.
You can use the reversed built-in method to reverse the ordering of your list of lists:
for li in reversed(lvl):
print li
Output:
[0, 0, 0, 0, 0]
[0, 0, 0, 0, 0]
[0, 0, 1, 0, 0]
[0, 0, 1, 0, 0]
[0, 0, 1, 0, 0]
If you're using for loops, you can use range to generate a reversed sequence to index lvl with.
>>> range(4,-1,-1)
[4, 3, 2, 1, 0]
i.e., maybe something similar to:
>>> for i in range(4,-1,-1):
... print lvl[i]
...
[0, 0, 0, 0, 0]
[0, 0, 0, 0, 0]
[0, 0, 1, 0, 0]
[0, 0, 1, 0, 0]
[0, 0, 1, 0, 0]
>>>