Printing lists onto tables in python

Question

If i had three lists such as

a = [1, 2, 3]
b = [4, 5, 6]
c = [7, 8, 9]

And wanted to print it like this

1  4  7
2  5  8
3  6  9

How would i do that?

meaby duplicated http://stackoverflow.com/questions/13214809/pretty-print-2d-python-list, http://stackoverflow.com/questions/9712085/numpy-pretty-print-tabular-data, http://stackoverflow.com/questions/5909873/python-pretty-printing-ascii-tables — gustavodiazjaimes, May 21 '13 at 19:28

score 8 · Answer 1 · answered May 21 '13 at 19:24

8

The hard part of this is transposing the array. But that's easy, with zip:

a = [1, 2, 3]
b = [4, 5, 6]
c = [7, 8, 9]
t = zip(a, b, c)

Now you just print it out:

print('\n'.join('  '.join(map(str, row)) for row in t))

answered May 21 '13 at 19:24

abarnert

2

IMHO, a very readable solution. I like keeping the zip separate (unlike other answers) because transposing and displaying are fundamentally different things to do. – Thane Brimhall May 21 '13 at 19:31

mgilson · Answer 2 · 2013-05-21T19:27:28.840

6

This should do it:

'\n'.join(' '.join(map(str,tup)) for tup in zip(a,b,c))

edited May 21 '13 at 19:27

answered May 21 '13 at 19:19

mgilson

3

+1, if for no other reason than you answered this in 36 seconds. – John May 21 '13 at 19:20
1

I think you want `' '`, because the OP has two spaces between columns. Or leave it as `' '` and do `str(x).ljust(2)` instead of `str`. – abarnert May 21 '13 at 19:22
Hold on, this is wrong… the OP is trying to print the lists transposed. – abarnert May 21 '13 at 19:23
This does not give output that OP asked for. – dansalmo May 21 '13 at 19:23
@abarnert -- Thanks. I didn't notice that until you mentioned it. – mgilson May 21 '13 at 19:41

pvoosten · Answer 3 · 2013-05-21T19:35:57.703

2

With ~~list comprehension~~ generator expression, without the map function:

'\n'.join(' '.join(str(y) for y in x) for x in zip(a,b,c))

edited May 21 '13 at 19:35

answered May 21 '13 at 19:29

pvoosten

First, in cases where all you're doing is mapping a nicely-named function that you already have lying around, why not use `map`? Yeah, it's less readable when you have to build a `lambda` or a `partial`, but in this case, I think it's _more_ readable. (Also, you don't have a list comprehension here, you have a generator expression.) – abarnert May 21 '13 at 19:33
@abarnert: you just answered your question yourself: map unnecessarily creates a list, which is not created because I use a generator expression (sorry for the faulty naming, edited that). A generator is cleaner than a list. I should also use the functional equivalent of zip, so add `from itertools import izip as zip` to the top of the script. – pvoosten May 21 '13 at 19:44
@pvoosten: Actually, `join` creates a list when you give it an iterator (at least with CPython and PyPy, probably with all implementations). Also, `map` doesn't create a list in 3.x. Most importantly, the performance implications of creating a list of 3 elements are so negligible that even having this discussion is silly. Use whichever one is more readable. – abarnert May 21 '13 at 20:05

3 Answers3