How do I combine two lists into one, while changing some of the values?

Question

I am working on my very first coding project, which is to make a text encoder. Once complete, I plan to make the decoder that will pair with it. For now, I am having trouble getting two lists to combine/overlap. I apologize if what I am about to show has an actual name that references it, I am new to coding and still learning many things.

list1 = [20.0, 'X', 'X', 46.0, 0.0, 18.0, 'X', 40.0]
list2 = ['Y', 31.0, 45.0, 'Y', 'Y', 'Y', 47.0, 'Y']

I need the output to be:

list3 = [20.0, 31.0, 45.0, 46.0, 0.0, 18.0, 47.0, 40.0]

Both lists have an equal number of values, and I need to combine them into one list, keep the numbers in their current order, and eliminate the "X"s and "Y"s entirely.

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Here is one way to iterate over the two lists simultaneously: https://stackoverflow.com/questions/21098350/python-iterate-over-two-lists-simultaneously?lq=1. You can use isintance(s, str) to test if s is a string. You can use list3.append(x) to append x to list3. Combine those and you will have a solution. — jarmod, Jul 03 '19 at 02:32

score 2 · Answer 1 · answered Jul 03 '19 at 02:34

2

Use zip with isinstance in a list-comprehension:

list1 = [20.0, 'X', 'X', 46.0, 0.0, 18.0, 'X', 40.0]
list2 = ['Y', 31.0, 45.0, 'Y', 'Y', 'Y', 47.0, 'Y']

list3 = [x if isinstance(x, float) else y for x, y in zip(list1, list2)]
# [20.0, 31.0, 45.0, 46.0, 0.0, 18.0, 47.0, 40.0]

answered Jul 03 '19 at 02:34

Austin

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Comprehension expressions, `zip` and `isinntance` are too advanced for a complete beginner. Simple loops and an accumulator are more appropriate. – Xero Smith Jul 03 '19 at 03:19
@Xero I have a little bit of familiarity with `zip`, even though I am still learning all of the different ways to implement it. but this is the first I am hearing of `isinstance`. – BrysonMG Jul 04 '19 at 04:16

score 1 · Answer 2 · answered Jul 03 '19 at 02:34

1

list1 = [20.0, 'X', 'X', 46.0, 0.0, 18.0, 'X', 40.0]
list2 = ['Y', 31.0, 45.0, 'Y', 'Y', 'Y', 47.0, 'Y']

list3 = []

for x in range(len(list1)):
    if isinstance(list1[x], float):
        list3.append(list1[x])

    else:
        list3.append(list2[x])

print(list3)

OUTPUT:-

[20.0, 31.0, 45.0, 46.0, 0.0, 18.0, 47.0, 40.0]

answered Jul 03 '19 at 02:34

Vasu Deo.S

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@jarmod can you please tell me why? – Vasu Deo.S Jul 03 '19 at 02:38
Your answer works, but is unpythonic. See https://python-forum.io/Thread-Basic-Never-use-for-i-in-range-len-sequence – jarmod Jul 03 '19 at 02:39
@jarmod Thanks for your suggestion. I would look forward to do as you mentioned in the later future. – Vasu Deo.S Jul 03 '19 at 02:45

edilio · Answer 3 · 2019-07-03T02:45:38.967

1

As @Austin said use zip to combine several lists of the same size.

Here is a version a little easier to understand if your new to development

def get_number(item1, item2):
    if item1 in ['X', 'Y']:
        return item2
    else:
        return item1

[get_number(x, y) for x, y in zip(list1, list2)]

OUTPUT:-

[20.0, 31.0, 45.0, 46.0, 0.0, 18.0, 47.0, 40.0]

edited Jul 03 '19 at 02:45

answered Jul 03 '19 at 02:39

edilio

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True we shouldn't be hardcoding values but in this case the problem is not clear. The problem says we need to eliminate Xs and Ys, it doesn't really states that it should be float values. So what happens if is really an `int` for example. – edilio Jul 03 '19 at 02:53

score 0 · Answer 4 · answered Jul 03 '19 at 02:46

0

Why not max with isinstance:

print([max(i, key=lambda x: isinstance(x, float)) for i in zip(list1, list2)])

Output:

[20.0, 31.0, 45.0, 46.0, 0.0, 18.0, 47.0, 40.0]

answered Jul 03 '19 at 02:46

U13-Forward

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1

This is not an obfuscation competition ;-) We're trying to teach basic Python to a beginner. – jarmod Jul 03 '19 at 02:47

MEOWWWWWWWW · Answer 5 · 2019-07-03T02:37:34.323

-2

list3 = [x if not str(x).isalpha() else list2[i] for i, x in enumerate(list1)]

verified

edited Jul 03 '19 at 02:37

answered Jul 03 '19 at 02:27

MEOWWWWWWWW

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Er, no. Did you test this? – jarmod Jul 03 '19 at 02:30
Your code results in the list [0, 1, 2, 3, 4, 5, 6, 7]. – doron Jul 03 '19 at 02:32
sorry for previous answer... I edited code and it works – MEOWWWWWWWW Jul 03 '19 at 02:39

Lê Tư Thành · Answer 6 · 2019-07-03T02:44:26.187

-2

This is a suggestion if you don't seriously care about the order of comnbined list

list1 = [20.0, 'X', 'X', 46.0, 0.0, 18.0, 'X', 40.0]
list2 = ['Y', 31.0, 45.0, 'Y', 'Y', 'Y', 47.0, 'Y']
a = list1 + list2
a = [x for x in a if not isinstance(x, str)]

>>>a
[20.0, 46.0, 0.0, 18.0, 40.0, 31.0, 45.0, 47.0]

edited Jul 03 '19 at 02:44

answered Jul 03 '19 at 02:35

Lê Tư Thành

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It does not output in the expected form. – Austin Jul 03 '19 at 02:36
@Austin, you mean the order of list? – Lê Tư Thành Jul 03 '19 at 02:38
That's not what the OP asked for. The output should be [20.0, 31.0, 45.0, 46.0, 0.0, 18.0, 47.0, 40.0]. – doron Jul 03 '19 at 02:39
@Austin, thanks for reminding. I edited my answer as a suggestion. – Lê Tư Thành Jul 03 '19 at 02:45

How do I combine two lists into one, while changing some of the values?

6 Answers6