How to change occurrence of the same element in a list next to each other without deleting the element in python?

Question

I have two lists list1=['A','B','C'] list2=['1','2','3'] I need a long list (combined by these 2 lists) of length 'n' without

1. any same pair consecutively ['A1','A1','C3','B2','B2',.....]
2. any same element of list1 consecutively ['A1','A2','A3','B1','B2',.......]
3. any same element of list2 consecutively ['A1','B1','C1','A2','B2',.......]

I want the elements of combined list in any order but without duplicates next to each other. In other words, exactly like this for this example, ['A1','B2','C3','A2','B3','C1','A3','B1','C2','A1','B2','C3'.....]

Can someone please help me. I am looking for an answer since 2 days.

Edit:

I tried itertools method products.

newlist = [ n[0]+n[1] for n in list(itertools.product(list1,list2))]

#This gives the exact permutation of elements I need but not in the order I wish.

newlist = ['a1','a2','a3','b1','b2','b3','c1','c2','c3']

#Then, I used nested loops,

#To swap consecutive pairs elements in the newlist for ind,n in enumerate(newlist): while n == newlist[ind-1]: for ind,n in enumerate(newlist): while n == newlist[ind-1]: newlist[ind-1],newlist[ind-2] = newlist[ind-2],newlist[ind-1]

#To swap consecutive list1 elements in the newlist for ind,n in enumerate(newlist): while n[0] == newlist[ind-1][0]: for ind,n in enumerate(newlist): while n[0] == newlist[ind-1][0]: newlist[ind-1],newlist[ind-2] = newlist[ind-2],newlist[ind-1]

#To swap consecutive list2 elements in the newlist for ind,n in enumerate(newlist): while n[1] == newlist[ind-1][1]: for ind,n in enumerate(newlist): while n[1] == newlist[ind-1][1]: newlist[ind-1],newlist[ind-2] = newlist[ind-2],newlist[ind-1]

Apparently, It works well with list with more than 3 elements. But not for the lists with length 3 and 2 respectively.

Answer 1

I have found a solution to what you want. A comment pointed by jrook showed a discussion similar to this but in their case it did not check to make sure it followed all the parameters you want. So i went ahead and wrote a little code for it.

import itertools

list1 = ["A","B","C"]
list2 = ["1","2","3", "4"]

if len(list1) < len(list2):
    x = list1[:]
    list1 = list2
    list2 = x
    list3 = [zip(x,list2) for x in itertools.permutations(list1,len(list2))]
    new = []
    for lis in list3:
        for i in lis:
            new.append(i[1] + i[0])    

else:
    list3 = [zip(x,list2) for x in itertools.permutations(list1,len(list2))]
    new = []
    for lis in list3:
        for i in lis:
            new.append(i[0] + i[1])



final = []
final.append(new[0])
new = new[1:]

def add_to(new, final):
    if final[-1][0] != new[0][0] and final[-1][1] != new[0][1] and final[-1] != new[0]:
        final.append(new[0])
        new = new[1:]
    else:
        b = new[0]
        new = new[1:]
        new.append(b)

    return new, final



while new != []:
    new, final = add_to(new, final)


print(final)

the variable final is a list that will make sure that all the rules u want are followed, i.e: no duplicates, none of the same consecutive letter or number. Hope this is what you were looking for. I edited this so that now you can have the second or first list be of longer length and it will work just fine.

Answer 2

#Join the given list
list(map("".join,(zip(["A", "B", "C"], ["1","2","3"]))))

# Given your list
l3=["A1","B1","C1","A2","B2"]
l2=["A1","A2","A3","B1","B2"]
l=["A1","A1","C3","B2","B2"]

# set() data structure ensure no duplicate
list(set(l))+list(set(l2))+list(set(l3))

# output should be:
# ['B2', 'C3', 'A1', 'B2', 'A3', 'A2', 'B1', 'A1', 'C1', 'B2', 'A2', 'B1', 'A1']

Hope this help.

Answer 3

#declaring 2 lists
    x=['a','b','c']
    y=[str(n) for n in range(1,5)]


    li=[]
    #Creating the pairs by shuffling two lists
    if len(x)>len(y):
        for m in range(len(x)):
            for n in range(len(y)):
                li.append(x[m]+y[n-1])
                m-=1
    else:
        for m in range(len(y)):
            for n in range(len(x)):
                li.append(y[m]+x[n-1])
                m-=1

    def pair_check(li):
        for ind,val in enumerate(li):
            if li[ind]==li[ind-1] or li[ind][0]==li[ind-1][0] or li[ind][1]==li[ind-1][1]:
                return True

    def pair_swap(li):
        for ind,val in enumerate(li):
            while li[ind]==li[ind-1] or li[ind][0]==li[ind-1][0] or li[ind][1]==li[ind-1][1]:
                li[ind-len(x)],li[ind]=li[ind],li[ind-(len(x))]

    #functions that verifies and swaps the pairs in combined list
    while pair_check(li):
        pair_swap(li)

    print (li)
    #Now the list li contains the list satisfies all the 3 conditions.