Create list of lists from list of numbers

Question

I'm working currently on a basic project, where I want to visualize later some data logged by some sensors.

I have a file with numbers:

75
0
0
30
35
32
38
45
53
44
51
62
43
34
56
42
28
32
43
56
43
46
16
33
48
...

And I want to create a list of lists, by every sub list will contain 6 element from the original ones, like [75,0,0,30,35,32],[38,45,53,44,51,62],...] .

f = open("log2.txt", "r")
content = f.readlines()
 
# Variable for storing the sum
idx = 0

line = []
db =  [] 

# Iterating through the content
for number in content:
    print(idx%6)
    if idx % 6 == 0:
        #newline
        db.append(line)
        line = []
        print("AAAAA")
    else:
        #continue line
        line.append(int(number))
    idx += idx+1

print(db)

But the result of db is only [[]] . Why? How can I do it well?

Answer 1

Taking inspiration from another answer here , we can provide a solution with lazy evaluation.

def chunks(lst, n):
    """Yield successive n-sized chunks from lst."""
    for i in range(0, len(lst), n):
        yield lst[i:i + n]


f = open("log2.txt", "r")
content = list(int(line) for line in f)

list_of_lists = list(chunks(content, 6))

Here we don't keep intermediate data in memory and this approach can be used to process very large files.

Answer 2

Method 1(List comprehension):

You can create a list comprehension looping through the lines of f :

f = open("log2.txt", "r")
content = f.readlines()
l = list(map(int, content)) # Converting each line to integer.
l = [l[i:i+6] for i in range(0,len(l), 6)] # Creating lists of 6 elements
print(l)

For eg, if a file contains:

1
2
3
4
5
6
7
8
9
10
11
12

Then the output is:

[[1, 2, 3, 4, 5, 6], [7, 8, 9, 10, 11, 12]]

Method 2(Improvements in your code):

f = open("log2.txt", "r")
content = f.readlines()
line = []
db =  [] 

# Iterating through the content
for idx, number in enumerate(content):
    if idx % 6 == 0:
        #newline
        line = [int(number)] # You need to add that number too!
        db.append(line)
    else:
        #continue line
        line.append(int(number))
print(db)

Output:

[[1, 2, 3, 4, 5, 6], [7, 8, 9, 10, 11, 12]]

What were you doing wrong?

1. Using a variable to keep track of the index. Instead, you can use enumerate() to get both the value and the index. Then you won't need to update or initialize idx .
2. You were not appending the number when idx % 6 == 0 .

Answer 3

f = open("log2.txt", "r", encoding='utf-8')
content = f.read()

content = content.split()
int_content = []
for i in content:
    int_content.append(int(i))

print(int_content)

final = []
# Iterating through the content
rng = 0
temp = []
for number in int_content:
    if rng != 6:
        temp.append(number)
        print(temp)
        range += 1
        continue
    else:
        rng = 0
        final.append(temp)
        temp = []

print(final)

Answer 4

There is much more simple way to do that:

f = open("log2.txt", "r")
content = f.readlines()

# now your content looks like this: ['75\n', '0\n', '0\n',...]
content = [int(x.strip()) for x in content]

# now your content looks like this [75, 0, 0, 30, 35, ...]

result = []
while content:
   result.append(content[:6])
   content = content[6:]

# now your result looks like this: [[75, 0, 0, 30, 35, 32], [38, 45, 53, 44, 51, 62],...]
# and your content variable is empty list