Python: CSV write by column rather than row
I have a python script that generates a bunch of data in a while loop. I need to write this data to a CSV file, so it writes by column rather than row.
For example in loop 1 of my script I generate:
(1, 2, 3, 4)
I need this to reflect in my csv script like so:
Result_1 1
Result_2 2
Result_3 3
Result_4 4
On my second loop i generate:
(5, 6, 7, 8)
I need this to look in my csv file like so:
Result_1 1 5
Result_2 2 6
Result_3 3 7
Result_4 4 8
and so forth until the while loop finishes. Can anybody help me?
EDIT
The while loop can last over 100,000 loops
The reason csv
doesn't support that is because variable-length lines are not really supported on most filesystems. What you should do instead is collect all the data in lists, then call zip()
on them to transpose them after.
>>> l = [('Result_1', 'Result_2', 'Result_3', 'Result_4'), (1, 2, 3, 4), (5, 6, 7, 8)]
>>> zip(*l)
[('Result_1', 1, 5), ('Result_2', 2, 6), ('Result_3', 3, 7), ('Result_4', 4, 8)]
wr.writerow(item) #column by column
wr.writerows(item) #row by row
This is quite simple if your goal is just to write the output column by column.
If your item is a list:
yourList = []
with open('yourNewFileName.csv', 'w', ) as myfile:
wr = csv.writer(myfile, quoting=csv.QUOTE_ALL)
for word in yourList:
wr.writerow([word])
Updating lines in place in a file is not supported on most file system (a line in a file is just some data that ends with newline, the next line start just after that).
As I see it you have two options:
- Have your data generating loops be generators, this way they won't consume a lot of memory - you'll get data for each row "just in time"
- Use a database (sqlite?) and update the rows there. When you're done - export to CSV
Small example for the first method:
from itertools import islice, izip, count
print list(islice(izip(count(1), count(2), count(3)), 10))
This will print
[(1, 2, 3), (2, 3, 4), (3, 4, 5), (4, 5, 6), (5, 6, 7), (6, 7, 8), (7, 8, 9), (8, 9, 10), (9, 10, 11), (10, 11, 12)]
even though count
generate an infinite sequence of numbers
what about Result_*
there also are generated in the loop (because i don't think it's possible to add to the csv file)
i will go like this ; generate all the data at one rotate the matrix write in the file:
A = []
A.append(range(1, 5)) # an Example of you first loop
A.append(range(5, 9)) # an Example of you second loop
data_to_write = zip(*A)
# then you can write now row by row