How to create a list of strings in python from two "array.flatten()"-ed lists

Question

I'm looking to create the following list in python:

list = ["pix420_615", "pix421_615", ... , "pix425_620"]

N.B. Where the list is a list of strings, not values.

From the following two lists:

x= [420, 421, 422, 423, 424, 425, 420, 421, 422, 423, 424, 425, 420, 421, 422, 423, 424, 425,
 420, 421, 422, 423, 424, 425, 420, 421, 422, 423, 424, 425, 420, 421, 422, 423, 424, 425]

y= [615, 615, 615, 615, 615, 615, 616, 616, 616, 616, 616, 616, 617, 617, 617, 617, 617, 617,
 618, 618, 618, 618, 618, 618, 619, 619, 619, 619, 619, 619, 620, 620, 620, 620, 620, 620]

I was wondering how I would go about doing this, and maintain the consistency of corresponding array values...?

Do you mean `list = ['pix420_615', 'pix421_615', ...]` where each element is a string? If not, what are the values `pix420_615`, etc.? — user94559, Jul 14 '16 at 16:38
@smarx Yeh, where each element is just a string created from adding pix to the x and y arrays in sequential order... — , Jul 14 '16 at 16:38
quite simply: `map(lambda t: 'pix%s_%s' % t, zip(x, y))` (or, if you don't like map: `['pix%s_%s' % t for t in zip(x, y)]`) — njzk2, Jul 14 '16 at 16:40

user94559 · Accepted Answer · 2016-07-14T16:42:33.367

This should do the trick. zip is the nicest way to do this sort of thing:

x = [420, 421, 422, 423, 424, 425, 420, 421, 422, 423, 424, 425, 420, 421, 422, 423, 424, 425, 420, 421, 422, 423, 424, 425, 420, 421, 422, 423, 424, 425, 420, 421, 422, 423, 424, 425]

y = [615, 615, 615, 615, 615, 615, 616, 616, 616, 616, 616, 616, 617, 617, 617, 617, 617, 617, 618, 618, 618, 618, 618, 618, 619, 619, 619, 619, 619, 619, 620, 620, 620, 620, 620, 620]

z = ['pix{}_{}'.format(a, b) for a, b in zip(x, y)]

print(z)

# Output:
# ['pix420_615', 'pix421_615', 'pix422_615', 'pix423_615', 'pix424_615', 'pix425_615', 'pix420_616', 'pix421_616', 'pix422_616', 'pix423_616', 'pix424_616', 'pix425_616', 'pix420_617', 'pix421_617', 'pix422_617', 'pix423_617', 'pix424_617', 'pix425_617', 'pix420_618', 'pix421_618', 'pix422_618', 'pix423_618', 'pix424_618', 'pix425_618', 'pix420_619', 'pix421_619', 'pix422_619', 'pix423_619', 'pix424_619', 'pix425_619', 'pix420_620', 'pix421_620', 'pix422_620', 'pix423_620', 'pix424_620', 'pix425_620']

score 2 · Answer 2 · answered Jul 14 '16 at 16:43

2

From your lists,

map(lambda t: 'pix%s_%s' % t, zip(x, y))

or

['pix%s_%s' % t for t in zip(x, y)]

However, I notice that the first list is basically [420, ..., 425], and the second one is [615, ...], which result in zip(x, y) representing the product of range(420, 426) and range(620, 626).

You can simplify all that by:

from itertools import product

['pix%s_%s' % (y, x) for x, y in product(range(615, 621), range(420, 426))]

answered Jul 14 '16 at 16:43

njzk2

38,969
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One *tiny* nit-pick. The small optimization benefit from using `map` over a list comprehension is lost [when using `lambda`](http://stackoverflow.com/a/1247490/1555990). I do like the `itertools.product` solution, though. – That1Guy Jul 14 '16 at 16:51

score 0 · Answer 3 · answered Jul 14 '16 at 16:44

0

use map function

map(lambda a, b: 'pix{0}_{1}'.format(a,b), x, y)

answered Jul 14 '16 at 16:44

Vishnu Upadhyay

5,043
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How to create a list of strings in python from two "array.flatten()"-ed lists

3 Answers3