I'm trying to make a function which concatenate multiple list if one element is the same in 2 or more different list.

Example :

[[1,2],[3,4,5],[0,4]] would become [[1,2],[0,3,4,5]

[[1],[1,2],[0,2]] would become [[0,1,2]]

[[1, 2], [2, 3], [3, 4]] would become [[1,2,3,4]]

In fact we just regroup the list if they have a common element and we delete one of the two element. The finals lists must have unique elements.

I tried to make the following function. It works, but when using big list (around 100 or 200 lists of list), I got the following recursion error :
RecursionError: maximum recursion depth exceeded while getting the repr of an object

def concat(L):
 break_cond = False
 print(L)
 for L1 in L:
 for L2 in L:
 if (bool(set(L1) & set(L2)) and L1 != L2):
 break_cond = True
 if (break_cond):
 i, j = 0, 0
 while i < len(L):
 while j < len(L):
 if (bool(set(L[i]) & set(L[j])) and i != j):
 L[i] = sorted(L[i] + list(set(L[j]) - set(L[i])))
 L.pop(j)
 j += 1
 i += 1
 return concat(L)

Moreover, I would like to do it using only basic python and not that much library. Any idea ? Thanks

Example of list where I get the error :

[[0, 64], [1, 120, 172], [2, 130], [3, 81, 102], [5, 126], [6, 176], [7, 21, 94], [8, 111, 167], [9, 53, 60, 138], [10, 102, 179], [11, 45, 72], [12, 53, 129], [14, 35, 40, 58, 188], [15, 86], [18, 70, 94], [19, 28], [20, 152], [21, 24], [22, 143, 154], [23, 110, 171], [24, 102, 144], [25, 73, 106, 187], [26, 189], [28, 114, 137], [29, 148], [30, 39], [31, 159], [33, 44, 132, 139], [34, 81, 100, 136, 185], [35, 53], [37, 61, 138], [38, 144, 147, 165], [41, 42, 174], [42, 74, 107, 162], [43, 99, 123], [44, 71, 122, 126], [45, 74, 144], [47, 94, 151], [48, 114, 133], [49, 130, 144], [50, 51], [51, 187], [52, 124, 142, 146, 167, 184], [54, 97], [55, 94], [56, 88, 128, 166], [57, 63, 80], [59, 89], [60, 106, 134, 142], [61, 128, 145], [62, 70], [63, 73, 76, 101, 106], [64, 80, 176], [65, 187, 198], [66, 111, 131, 150], [67, 97, 128, 159], [68, 85, 128], [69, 85, 169], [70, 182], [71, 123], [72, 85, 94], [73, 112, 161], [74, 93, 124, 151, 191], [75, 163], [76, 99, 106, 129, 138, 152, 179], [77, 89, 92], [78, 146, 156], [79, 182], [82, 87, 130, 179], [83, 148], [84, 110, 146], [85, 98, 137, 177], [86, 198], [87, 101], [88, 134, 149], [89, 99, 107, 130, 193], [93, 147], [95, 193], [96, 98, 109], [104, 105], [106, 115, 154, 167, 190], [107, 185, 193], [111, 144, 153], [112, 128, 188], [114, 136], [115, 146], [118, 195], [119, 152], [121, 182], [124, 129, 177], [125, 156], [126, 194], [127, 198], [128, 149], [129, 153], [130, 164, 196], [132, 140], [133, 181], [135, 165, 170, 171], [136, 145], [141, 162], [142, 170, 187], [147, 171], [148, 173], [150, 180], [153, 191], [154, 196], [156, 165], [157, 177], [158, 159], [159, 172], [161, 166], [162, 192], [164, 184, 197], [172, 199], [186, 197], [187, 192]]

As mentioned by @ScottBoston this is a graph problem, known as connected components, I suggest you used networkx as indicated by @ScottBoston, in case you cannot here is a version without networkx:

from itertools import combinations


def bfs(graph, start):
 visited, queue = set(), [start]
 while queue:
 vertex = queue.pop(0)
 if vertex not in visited:
 visited.add(vertex)
 queue.extend(graph[vertex] - visited)
 return visited


def connected_components(G):
 seen = set()
 for v in G:
 if v not in seen:
 c = set(bfs(G, v))
 yield c
 seen.update(c)


def graph(edge_list):
 result = 
 for source, target in edge_list:
 result.setdefault(source, set()).add(target)
 result.setdefault(target, set()).add(source)
 return result


def concat(l):
 edges = 
 s = list(map(set, l))
 for i, j in combinations(range(len(s)), r=2):
 if s[i].intersection(s[j]):
 edges.append((i, j))
 G = graph(edges)

 result = 
 unassigned = list(range(len(s)))
 for component in connected_components(G):
 union = set().union(*(s[i] for i in component))
 result.append(sorted(union))
 unassigned = [i for i in unassigned if i not in component]

 result.extend(map(sorted, (s[i] for i in unassigned)))

 return result


print(concat([[1, 2], [3, 4, 5], [0, 4]]))
print(concat([[1], [1, 2], [0, 2]]))
print(concat([[1, 2], [2, 3], [3, 4]]))

Output

[[0, 3, 4, 5], [1, 2]]
[[0, 1, 2]]
[[1, 2, 3, 4]]

You can use networkx library because is a graph theory and connected components problem:

import networkx as nx

l = [[1,2],[3,4,5],[0,4]]
#l = [[1],[1,2],[0,2]]
#l = [[1, 2], [2, 3], [3, 4]]

G = nx.Graph()

#Add nodes to Graph 
G.add_nodes_from(sum(l, ))

#Create edges from list of nodes
q = [[(s[i],s[i+1]) for i in range(len(s)-1)] for s in l]

for i in q:

 #Add edges to Graph
 G.add_edges_from(i)

#Find all connnected components in graph and list nodes for each component
[list(i) for i in nx.connected_components(G)]

Output:

[[1, 2], [0, 3, 4, 5]]

Output if uncomment line 2 and comment line 1:

[[0, 1, 2]]

Likewise for line 3:

[[1, 2, 3, 4]]

Here's an iterative approach, should be about as efficient as you can probably get in pure python. One thing is having to spend an extra pass removing duplicates at the end.

original_list = [[1,2],[3,4,5],[0,4]]

mapping = 
rev_mapping = 

for i, candidate in enumerate(original_list):
 sentinel = -1
 for item in candidate:
 if mapping.get(item, -1) != -1:
 merge_pos = mapping[item]
 #update previous list with all new candidates
 for item in candidate:
 mapping[item] = merge_pos
 rev_mapping[merge_pos].extend(candidate)
 break
 else:
 for item in candidate:
 mapping[item] = i
 rev_mapping.setdefault(i, ).extend(candidate)

result = [list(set(item)) for item in rev_mapping.values()]
print(result)

Output:

[[1, 2], [0, 3, 4, 5]]

You can use a recursive version of the breadth-first search with no imports:

def group_vals(d, current, _groups, _seen, _master_seen):
 if not any(set(current)&set(i) for i in d if i not in _seen):
 yield list(i for b in _groups for i in b)
 for i in d:
 if i not in _master_seen:
 yield from group_vals(d, i, [i], [i], _master_seen+[i])
 else:
 for i in d:
 if i not in _seen and set(current)&set(i):
 yield from group_vals(d, i, _groups+[i], _seen+[i], _master_seen+[i])

def join_data(_data):
 _final_result = list(group_vals(_data, _data[0], [_data[0]], [_data[0]], ))
 return [a for i, a in enumerate(_final_result) if a not in _final_result[:i]]

c = [[[1,2],[3,4,5],[0,4]], [[1],[1,2],[0,2]], [[1, 2], [2, 3], [3, 4]]]
print(list(map(join_data, c)))

Output:

[
 [[1, 2], [0, 3, 4, 5]], 
 [[0, 1, 2]], 
 [[1, 2, 3, 4]]
]

if you want it in simple form here is solution :

def concate(l):
 len_l = len(l)
 i = 0
 while i < (len_l - 1):
 for j in range(i + 1, len_l):

 # i,j iterate over all pairs of l's elements including new 
 # elements from merged pairs. We use len_l because len(l)
 # may change as we iterate

 i_set = set(l[i])
 j_set = set(l[j])

 if len(i_set.intersection(j_set)) > 0:
 # Remove these two from list
 l.pop(j)
 l.pop(i)

 # Merge them and append to the orig. list
 ij_union = list(i_set.union(j_set))
 l.append(ij_union)

 # len(l) has changed
 len_l -= 1

 # adjust 'i' because elements shifted
 i -= 1

 # abort inner loop, continue with next l[i]
 break

 i += 1
 return l