I have a matrix:
matrix = [['F', 'B', 'F', 'A', 'C', 'F'],
['D', 'E', 'B', 'E', 'B', 'E'],
['F', 'A', 'D', 'B', 'F', 'B'],
['B', 'E', 'F', 'B', 'D', 'D']]
I want to remove and collect the first two elements of each sub-list, and add them to a new list.
so far i have got:
while messagecypher:
for vector in messagecypher:
final.extend(vector[:2])
the problem is; the slice doesn't seem to remove the elements, and I end up with a huge list of repeated chars. I could use .pop(0) twice, but that isn't very clean.
NOTE: the reason i remove the elements is becuase i need to keep going over each vector until the matrix is empty
You can keep your slice and do:
final = []
for i in range(len(matrix)):
matrix[i], final = matrix[i][:2], final + matrix[i][2:]
Note that this simultaneously assigns the sliced list back to matrix and adds the sliced-off part to final.
Well you can use a list comprehension to get the thing done, but its perhaps counter-intuitive:
>>> matrix = [['F', 'B', 'F', 'A', 'C', 'F'],
['D', 'E', 'B', 'E', 'B', 'E'],
['F', 'A', 'D', 'B', 'F', 'B'],
['B', 'E', 'F', 'B', 'D', 'D']]
>>> while [] not in matrix: print([i for var in matrix for i in [var.pop(0), var.pop(0)]])
['F', 'B', 'D', 'E', 'F', 'A', 'B', 'E']
['F', 'A', 'B', 'E', 'D', 'B', 'F', 'B']
['C', 'F', 'B', 'E', 'F', 'B', 'D', 'D']
EDIT:
Using range makes the syntax look cleaner:
>>> matrix = [['C', 'B', 'B', 'D', 'F', 'B'], ['D', 'B', 'B', 'A', 'B', 'A'], ['B', 'D', 'E', 'F', 'C', 'B'], ['B', 'A', 'C', 'B', 'E', 'F']]
>>> while [] not in matrix: print([var.pop(0) for var in matrix for i in range(2)])
['C', 'B', 'D', 'B', 'B', 'D', 'B', 'A']
['B', 'D', 'B', 'A', 'E', 'F', 'C', 'B']
['F', 'B', 'B', 'A', 'C', 'B', 'E', 'F']
Deleting elements is not an efficient way to go about your task. It requires Python to perform a lot of unnecessary work shifting things around to fill the holes left by the deleted elements. Instead, just shift your slice over by two places each time through the loop:
final = []
for i in xrange(0, len(messagecypher[0]), 2):
for vector in messagecypher:
final.extend(vector[i:i+2])
Related
I created 2 lists in python `
ls = []
a = ['a','b','c','d','e','f']
i = 0
while i < 5:
x = a[-1]
a.pop(-1)
a.insert(0, x)
ls.insert(0, a)
i += 1
print(ls)
What I want to do is to add something from the list filled with letters into an empty list and making the result look like this
ls = [
['a','b','c','d','e','f'],
['f','a','b','c','d','e'],
['e','f','a','b','c','d'],
['d','e','f','a','b','c'],
['c','d','e','f','a','b'],
['b','c','d','e','f','a']
]
I would like to know where I made a mistake in python and the solution.
The list is a mutable object in python, so when you insert the list a in the ls, you are just adding a reference to the list a, instead of adding the whole value.
A workaround would be to insert a copy of a in the ls. One way to create a new copy of the list is using the list() on the list or you can use copy function from copy module. So doing ls.insert(0, a.copy()) would give the same result as below -
ls = []
a = ['a','b','c','d','e','f']
i = 0
while i < 5:
x = a[-1]
a.pop(-1)
a.insert(0, x)
ls.insert(0, list(a)) # updated this
i += 1
print(ls)
Output:
[['b', 'c', 'd', 'e', 'f', 'a'], ['c', 'd', 'e', 'f', 'a', 'b'], ['d', 'e', 'f', 'a', 'b', 'c'], ['e', 'f', 'a', 'b', 'c', 'd'], ['f', 'a', 'b', 'c', 'd', 'e']]
Another easy way to get your expected output would be to -
ls = []
a = ['a','b','c','d','e','f']
for i in range(6):
ls.append(a.copy())
a = [a[-1]] + a[:-1]
print(ls)
Output :
[['a', 'b', 'c', 'd', 'e', 'f'], ['f', 'a', 'b', 'c', 'd', 'e'], ['e', 'f', 'a', 'b', 'c', 'd'], ['d', 'e', 'f', 'a', 'b', 'c'], ['c', 'd', 'e', 'f', 'a', 'b'], ['b', 'c', 'd', 'e', 'f', 'a']]
Rows = int(input("give the number of rows:"))
Columns = int(input("Give the number of columns:"))
matrix = []
for i in range(Rows):
matrix.append(['a', 'b', 'c','d', 'e'])
for vector in matrix:
print(matrix)
here's the output:
give the number of rows:3
Give the number of columns:3
[['a', 'b', 'c', 'd', 'e']]
[['a', 'b', 'c', 'd', 'e'], ['a', 'b', 'c', 'd', 'e']]
[['a', 'b', 'c', 'd', 'e'], ['a', 'b', 'c', 'd', 'e']]
[['a', 'b', 'c', 'd', 'e'], ['a', 'b', 'c', 'd', 'e'], ['a', 'b', 'c', 'd', 'e']]
[['a', 'b', 'c', 'd', 'e'], ['a', 'b', 'c', 'd', 'e'], ['a', 'b', 'c', 'd', 'e']]
[['a', 'b', 'c', 'd', 'e'], ['a', 'b', 'c', 'd', 'e'], ['a', 'b', 'c', 'd', 'e']]
[it needed to be like this when the user input the rows and columns 3x3]
a b c
d e f
g h i
There are many ways to initalize an array with a specific size. Below is one of the more concise ways.
Rows = int(input("Give the number of rows:"))
Columns = int(input("Give the number of columns:"))
matrix = [["a"]*Rows]*Columns
print(matrix)
This will give the output
Give the number of rows:3
Give the number of columns:3
[['a', 'a', 'a'], ['a', 'a', 'a'], ['a', 'a', 'a']]
This gives the array sizing that you are looking for.
I have following sequence of data:
['A',
'A',
'A',
'A',
'A',
'A',
'A',
'D',
'D',
'D',
'D',
'D',
'D',
'A',
'A',
'A',
'A',
'A',
'D',
'D',
'D',
'D',
'D',
'D']
How would I be able to create subsequence (list of list) as an example:
[['A',
'A',
'A',
'A',
'A',
'A',
'A'],
['D',
'D',
'D',
'D',
'D',
'D'],
['A',
'A',
'A',
'A',
'A'], ['D',
'D',
'D',
'D', 'D', 'D']]
That is I want to create a sublist which accumulates the first encountered value (eg 'A' or 'D' and append that to sublist and continue until it arrives at a different alphabet. The second list contains the sequence of the letters that were different than the first sequence and appends as sublist. The process continues until the last element of the main list.
itertools.groupby is a good tool for this kind of tasks:
from itertools import groupby
lst = ['A', 'A', 'A', 'A', 'A', 'A', 'A', 'D', 'D', 'D', 'D', 'D', 'D', 'A', 'A', 'A', 'A', 'A', 'D', 'D', 'D', 'D', 'D', 'D']
output = [list(g) for _, g in groupby(lst)]
print(output)
# [['A', 'A', 'A', 'A', 'A', 'A', 'A'], ['D', 'D', 'D', 'D', 'D', 'D'], ['A', 'A', 'A', 'A', 'A'], ['D', 'D', 'D', 'D', 'D', 'D']]
Solution:
import itertools
lis = ['A', 'A', 'A', 'A', 'A', 'A', 'A', 'D', 'D', 'D', 'D', 'D', 'D', 'A', 'A', 'A', 'A', 'A', 'D', 'D', 'D', 'D', 'D', 'D']
print([list(x[1]) for x in itertools.groupby(lis)])
Output:
[['A', 'A', 'A', 'A', 'A', 'A', 'A'], ['D', 'D', 'D', 'D', 'D', 'D'], ['A', 'A', 'A', 'A', 'A'], ['D', 'D', 'D', 'D', 'D', 'D']]
I have a list of lists containing unique strings and I want to produce an arbitrary number of different ways of sorting it. The list might look like the following:
list = [[a], [b,c], [d], [e,f,g]]
The order of the lists need to be the same but I want to shuffle the ordering within a list and then have them in a single list, e.g
list1 = [a,b,c,d,e,f,g]
list2 = [a,c,b,d,f,e,g]
...
...
listN = [a,c,b,d,f,g,e]
What is a good pythonic way of achieving this? I'm on python 2.7.
from itertools import permutations, product
L = [['a'], ['b','c'], ['d'], ['e', 'f', 'g']]
for l in product(*map(lambda l: permutations(l), L)):
print([item for s in l for item in s])
produces:
['a', 'b', 'c', 'd', 'e', 'f', 'g']
['a', 'b', 'c', 'd', 'e', 'g', 'f']
['a', 'b', 'c', 'd', 'f', 'e', 'g']
['a', 'b', 'c', 'd', 'f', 'g', 'e']
['a', 'b', 'c', 'd', 'g', 'e', 'f']
['a', 'b', 'c', 'd', 'g', 'f', 'e']
['a', 'c', 'b', 'd', 'e', 'f', 'g']
['a', 'c', 'b', 'd', 'e', 'g', 'f']
['a', 'c', 'b', 'd', 'f', 'e', 'g']
['a', 'c', 'b', 'd', 'f', 'g', 'e']
['a', 'c', 'b', 'd', 'g', 'e', 'f']
['a', 'c', 'b', 'd', 'g', 'f', 'e']
You can do this by taking the Cartesian product of the permutations of the sub-lists, and then flattening the resulting nested tuples.
from itertools import permutations, product, chain
lst = [['a'], ['b', 'c'], ['d'], ['e', 'f', 'g']]
for t in product(*[permutations(u) for u in lst]):
print([*chain.from_iterable(t)])
output
['a', 'b', 'c', 'd', 'e', 'f', 'g']
['a', 'b', 'c', 'd', 'e', 'g', 'f']
['a', 'b', 'c', 'd', 'f', 'e', 'g']
['a', 'b', 'c', 'd', 'f', 'g', 'e']
['a', 'b', 'c', 'd', 'g', 'e', 'f']
['a', 'b', 'c', 'd', 'g', 'f', 'e']
['a', 'c', 'b', 'd', 'e', 'f', 'g']
['a', 'c', 'b', 'd', 'e', 'g', 'f']
['a', 'c', 'b', 'd', 'f', 'e', 'g']
['a', 'c', 'b', 'd', 'f', 'g', 'e']
['a', 'c', 'b', 'd', 'g', 'e', 'f']
['a', 'c', 'b', 'd', 'g', 'f', 'e']
If you need to do this in Python 2, you can replace the print line with this:
print list(chain.from_iterable(t))
Here's a more compact version, inspired by ewcz's answer:
for t in product(*map(permutations, lst)):
print list(chain.from_iterable(t))
This might not be the most elegant solution, but I think it does what you want
from itertools import permutations
import numpy as np
def fac(n):
if n<=1:
return 1
else:
return n * fac(n-1)
lists = [['a'], ['b','c'], ['d'], ['e','f','g']]
combined = [[]]
for perm in [permutations(l,r=len(l)) for l in lists]:
expanded = []
for e in list(perm):
expanded += [list(l) + list(e) for l in combined]
combined = expanded
## check length
print np.prod(map(fac,map(len,lists))), len(combined)
print '\n'.join(map(str,combined))
You can flatten the list then simply generate its permutations:
from itertools import chain, permutations
li = [['a'], ['b','c'], ['d'], ['e','f','g']]
flattened = list(chain.from_iterable(li))
for perm in permutations(flattened, r=len(flattened)):
print(perm)
>> ('a', 'b', 'c', 'd', 'e', 'f', 'g')
('a', 'b', 'c', 'd', 'e', 'g', 'f')
('a', 'b', 'c', 'd', 'f', 'e', 'g')
('a', 'b', 'c', 'd', 'f', 'g', 'e')
('a', 'b', 'c', 'd', 'g', 'e', 'f')
('a', 'b', 'c', 'd', 'g', 'f', 'e')
('a', 'b', 'c', 'e', 'd', 'f', 'g')
('a', 'b', 'c', 'e', 'd', 'g', 'f')
('a', 'b', 'c', 'e', 'f', 'd', 'g')
...
...
...
from itertools import chain, permutations
your_list = [[a], [b,c], [d], [e,f,g]]
flattened = chain.from_iterable(your_list)
perms = permutations(flattened)
for perm in perms:
print perm
References:
permutations in Python 2
chain in Python 2
Currently working on a 2D transposition cipher in Python. So I have a list that contains an encoded message, like below:
['BF', 'AF', 'AF', 'DA', 'CD', 'DD', 'BC', 'EF', 'DA', 'AA', 'EF', 'BF']
The next step is taking that list, splitting it up and putting it into a new matrix with regards to a keyword that the user enters. Which I have below:
Enter the keyword for final encryption: hide
H I D E
['B', 'F', 'A', 'F']
['A', 'F', 'D', 'A']
['C', 'D', 'D', 'D']
['B', 'C', 'E', 'F']
['D', 'A', 'A', 'A']
['E', 'F', 'B', 'F']
What I would like to do next and haven't done is take each of the columns above and print them in alphabetical order, therefore getting another cipher text, like below:
D E H I
['A', 'F', 'B', 'F']
['D', 'A', 'A', 'F']
['D', 'D', 'C', 'D']
['E', 'F', 'B', 'C']
['A', 'A', 'D', 'A']
['B', 'F', 'E', 'F']
Here's my code:
def encodeFinalCipher():
matrix2 = []
# Convert keyword to upper case
keywordKey = list(keyword.upper())
# Convert firstEncryption to a string
firstEncryptionString = ''.join(str(x) for x in firstEncryption)
# Print the first table that will show the firstEncryption and the keyword above it
keywordList = list(firstEncryptionString)
for x in range(0,len(keywordList),len(keyword)):
matrix2.append(list(keywordList[x:x+len(keyword)]))
# Print the matrix to the screen
print (' %s' % ' '.join(map(str, keywordKey)))
for letters in matrix2:
print (letters)
return finalEncryption
I have traversed the 2D matrix and got all the column entries like below:
b = [[matrix2[i][j] for i in range(len(matrix2))] for j in range(len(matrix2[0]))]
for index, item in enumerate (b):
print("\n",index, item)
OUTPUT:------
0 ['B', 'A', 'C', 'B', 'D', 'E']
1 ['F', 'F', 'D', 'C', 'A', 'F']
2 ['A', 'D', 'D', 'E', 'A', 'B']
3 ['F', 'A', 'D', 'F', 'A', 'F']
How would I append each letter of the keywordKey (e.g. 'H' 'I' 'D' 'E') to the list where the numbers 0,1,2,3 are?
Or probably a more efficient solution. How would I put the letters into the keywordKey columns when creating the matrix? Would a dictionary help here? Then I could sort the dictionary and print the final cipher.
Many thanks
You can do something like this:
>>> from operator import itemgetter
>>> from pprint import pprint
>>> lst = [['B', 'F', 'A', 'F'],
['A', 'F', 'D', 'A'],
['C', 'D', 'D', 'D'],
['B', 'C', 'E', 'F'],
['D', 'A', 'A', 'A'],
['E', 'F', 'B', 'F']]
>>> key = 'HIDE'
Sort xrange(len(key)) or range(len(key)) using the corresponding values from key and then you will have a list of indices:
>>> indices = sorted(xrange(len(key)), key=key.__getitem__)
>>> indices
[2, 3, 0, 1]
Now all we need to do is loop over the list and apply these indices to each item using operator.itemgetter and get the corresponding items:
>>> pprint([list(itemgetter(*indices)(x)) for x in lst])
[['A', 'F', 'B', 'F'],
['D', 'A', 'A', 'F'],
['D', 'D', 'C', 'D'],
['E', 'F', 'B', 'C'],
['A', 'A', 'D', 'A'],
['B', 'F', 'E', 'F']]
#or simply
>>> pprint([[x[i] for i in indices] for x in lst])
[['A', 'F', 'B', 'F'],
['D', 'A', 'A', 'F'],
['D', 'D', 'C', 'D'],
['E', 'F', 'B', 'C'],
['A', 'A', 'D', 'A'],
['B', 'F', 'E', 'F']]