Pythonic Way to Sum List of Lists of Strings

Question

I’ve found a way to do what I want which is, But I’m wondering if there’s a way I can get this down to one line.

I have a list of list of lists of strings, as compared to a lists of numbers (for which there’s an answer: [Sum of list of lists; returns sum list)

Example List:

list = [['T=-40F A=0K', 'T=-15F A=0K', 'T=59F A=0K', 'T=98F A=0K', 'T=120F A=0K'],
 ['T=-40F A=10K','T=-15F A=10K','T=59F A=10K','T=98F A=10K','T=120F A=10K']]

Example Output:

['T=-40F A=0K', 'T=-15F A=0K', 'T=59F A=0K', 'T=98F A=0K', 'T=120F A=0K', 'T=-40F A=10K', 'T=-15F A=10K', 'T=59F A=10K', 'T=98F A=10K', 'T=120F A=10K']

I can join these with this method:

new = []
for i in [['T=%.0fF A=%.0fK'%(t,a)for t in TEMP] for a in ALT]:
    new = new + i

Anyone got anything?

As for the application im adding a legend to a matplotlib plot

This would be really easy, and an awesome feature with sum(list)

Asked By: Kevin R.

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Source

Answer 1

Using List Comprehension:

>>> my_list = [['T=-40F A=0K', 'T=-15F A=0K', 'T=59F A=0K', 'T=98F A=0K', 'T=120F A=0K'], ['T=-40F A=10K','T=-15F A=10K','T=59F A=10K','T=98F A=10K','T=120F A=10K']]
>>>
>>> [y for x in my_list for y in x]
['T=-40F A=0K', 'T=-15F A=0K', 'T=59F A=0K', 'T=98F A=0K', 'T=120F A=0K', 'T=-40F A=10K', 'T=-15F A=10K', 'T=59F A=10K', 'T=98F A=10K', 'T=120F A=10K']

And you should not use list as your variable name.

Answered By: Rohit Jain

Answer 2

You want to flatten the iterable – itertools.chain.from_iterable() exists for that very purpose:

>>> data = ...
>>> import itertools
>>> list(itertools.chain.from_iterable(data))
['T=-40F A=0K', 'T=-15F A=0K', 'T=59F A=0K', 'T=98F A=0K', 'T=120F A=0K', 'T=-40F A=10K', 'T=-15F A=10K', 'T=59F A=10K', 'T=98F A=10K', 'T=120F A=10K']

It returns an iterator, so you can use list() if you need a list, or just use the iterator.

Answered By: Gareth Latty

Answer 3

You can flatten the list using itertools.chain().

>>> testList =[['T=-40F A=0K', 'T=-15F A=0K', 'T=59F A=0K', 'T=98F A=0K', 'T=120F A=0K'],
 ['T=-40F A=10K','T=-15F A=10K','T=59F A=10K','T=98F A=10K','T=120F A=10K']]
>>> 
>>> from itertools import chain
>>> chain(*testList)
<itertools.chain object at 0x02B1E910>
>>> list(chain(*testList))
['T=-40F A=0K', 'T=-15F A=0K', 'T=59F A=0K', 'T=98F A=0K', 'T=120F A=0K', 'T=-40F A=10K', 'T=-15F A=10K', 'T=59F A=10K', 'T=98F A=10K', 'T=120F A=10K']

OR Use itertools.chain.from_iterable()

>>> list(chain.from_iterable(testList))
['T=-40F A=0K', 'T=-15F A=0K', 'T=59F A=0K', 'T=98F A=0K', 'T=120F A=0K', 'T=-40F A=10K', 'T=-15F A=10K', 'T=59F A=10K', 'T=98F A=10K', 'T=120F A=10K']

P.S – Please don’t use list as a variable name, it shadows the builtin.

Answered By: Sukrit Kalra

Answer 4

Try itertools.chain.fromiterable() –

from itertools import chain
result = list(chain.from_iterable(your_list))

Answered By: svineet

Pythonic Way to Sum List of Lists of Strings

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