Merge different lists together in Python

Question

I am so called newbie in Python. I have difficulties with lists. I have a loop which take some info from textfile and goes through function. If textfiles lenght is 10 rows then output will be 10 separate lists, like that: [0.45] [0.87] ... and so on, for n+1 times(it depends how long textfile is).

How can I put them into single list, like [0.45, 0.87, ...]? I experimented with different loops but nothing :(

I am previously thankfull :) .. and sry about my bad english

Code:

from pyfann import libfann
import os
path="."
ext = ".net"
files = [file for file in os.listdir(path) if file.lower().endswith(ext)]
for j in files:
 ann = libfann.neural_net()
 ann.create_from_file(j)
 print j
 f=open('nsltest1.dat','r')
 for i in f:
  x=i.strip()
  y=[float(i) for i in x.split()]
  z=ann.run(y)
  print z

Possible duplicate of How to append list to second list (concatenate lists) — janot
– janot, Commented Apr 16, 2016 at 11:03

jdotjdot · Accepted Answer · 2012-11-20 20:41:32Z

11

If you have all of your lists stored in a list a,

# a = [[.45], [.87], ...]
import itertools
output = list(itertools.chain(*a))

What makes this answer better than the others is that it neatly joins an arbitrary number of lists together in one line, without a need for a for loop or anything like that.

answered Nov 20, 2012 at 20:41

jdotjdot

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3 Comments

mutionu Over a year ago

That's the problem, I do not know how to join them to another list

jdotjdot Over a year ago

Well, your code is a little convoluted to begin with, but what you could do is outside looping through the text you could instantiate a variable listoflists = [] and then in the for loop add each list item to the list with listoflists.append(...) or listoflists += <item> or listoflists.extend(...) depending on what you're trying to do. This might help.

affhendrawan Over a year ago

sir, what is "*" means ?

Community · Accepted Answer · 2017-05-23 12:25:13Z

3

You might want to have a look at the following questions:

Basically, if you're reading your lines in a loop, you can do like

result = []
for line in file:
    newlist = some_function(line) # newlist contains the result list for the current line
    result = result + newlist

edited May 23, 2017 at 12:25

CommunityBot

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answered Nov 20, 2012 at 20:44

MartinStettner

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1 Comment

mutionu Over a year ago

Thank you, it gives me screen full of lines but I try to it more suitable for me.

score 3 · Accepted Answer · 2012-11-20 20:46:24Z

3

Addition operator + is what you might want.

list1 = [1, 2, 3]
list2 = [4, 5, 6]
merged_list = list1 + list2
print(merged_list) #replace ( and ) with spaces if you're using python 2.x

Will output [1, 2, 3, 4, 5, 6]

edited Nov 20, 2012 at 20:46

answered Nov 20, 2012 at 20:40

user1632861

Comments

mgilson · Accepted Answer · 2012-11-20 20:43:09Z

1

You can just add them: [1] + [2] = [1, 2].

edited Nov 20, 2012 at 20:43

mgilson

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answered Nov 20, 2012 at 20:40

alestanis

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