how to combine multiple lines from multiple files and put them to an array

Question

I have three text files each file contain text like this

file1.txt
    a1
    a2
    a3

file2.txt
    b1
    b2

file3
    c1
    c2

I need to add them to an array like this

[[a1,b1,c1] , [a1,b1,c2] , [a1,b2,c1] , [a1,b2,c2] , [a2,c1,b1] , ....]

my code here

list1 = []
x = open('../f1.txt')
y = open('../f2.txt')
z = open('../f3.txt')
for a in x:
  for b in y:
    for c in z:
        list1.append((a.strip() , b.strip(), c.stip()))



for w in list1:
  print w

it combine just first line in x with first line in y with all lines in z

Answer 1

Here is an approach to solve your problem using combinations and chain from itertools module:

from itertools import combinations, chain


def read_from_files(files):
    """Read all the files"""
    for _file in files:
        with open(_file, 'r') as f:
            # remove `\n` from the end of lines
            yield [elm.strip('\n') for elm in f.readlines()]


def get_output(data, n=3):
    """return combinations based on `n`"""
    # chain the data to get a full list of items
    return combinations(chain.from_iterable(data), n)


files = ['file1', 'file2', 'file3']
data = read_from_files(files)
output = list(get_output(data))
print(output)

Output:

[('a1', 'a2', 'a3'), ('a1', 'a2', 'b1'), ('a1', 'a2', 'b2'), ('a1', 'a2', 'b3'), ('a1', 'a2', 'c1'), ('a1', 'a2', 'c2'), ('a1', 'a3', 'b1'), ('a1', 'a3', 'b2'),
...

('b1', 'b2', 'c2'), ('b1', 'b3', 'c1'), ('b1', 'b3', 'c2'), ('b1', 'c1', 'c2'), ('b2', 'b3', 'c1'), ('b2', 'b3', 'c2'), ('b2', 'c1', 'c2'), ('b3', 'c1', 'c2')]

Answer 2

When you iterate of a File object, you can only iterate on it once. When the 3 lines of z are read, the y for loop goes to the next line in f2 . However the iteration ends since there is no other line to read in f3 .

One solution would be to re-open the files at all iterations, but that's not very sexy. I suggest reading the three files in the opening call directly.

My version :

list1 = []
lines = []
for file in ['f1', 'f2', 'f3']:
    with open(file) as f:
        lines.append(f.readlines())
for xline in lines[0]:
    for yline in lines[1]:
        for zline in lines[2]:
            list1.append((xline.strip(), yline.strip(), zline.strip()))