Creating nested lists from a single list

Question

Suppose I have a list like this:

my_list = ['a_norm', 'a_std', 'a_min', 'a_max', 'a_flag', 'b_norm', 'b_std', 'b_min', 'b_max', 'b_flag', 'c_norm', 'c_std', 'c_min', 'c_max', 'c_flag']

I want to parse this list and create nested lists within separate lists like this. It is very important that I retain the order of the :

a_list = [[1, "a_norm"], [2, "a_std"], [3, "a_min"], [4, "a_max"], [5, "a_flag"]]
b_list = [[1, "b_norm"], [2, "b_std"], [3, "b_min"], [4, "b_max"], [5, "b_flag"]]
c_list = [[1, "c_norm"], [2, "c_std"], [3, "c_min"], [4, "c_max"], [5, "c_flag"]]

I tried the below which, in addition to being convoluted, did not work (endless loop). Any suggestions on how to accomplish my end goal?

a_list = []
b_list = []
c_list = []
i = 1
j = 1
k = 1
while (i < 6) and (j < 6) and (k < 6):
    for item in my_list:
        if 'a' in item:
            a_list.append(i)
            a_list.append(item)
            i + 1
        elif 'b' in my_list:
            b_list.append(j)
            b_list.append(item)
            j + 1
        elif 'c' in my_list:
            c_list.append(k)
            c_list.append(item)
            k + 1

depend on what you order the values like (a_norm , a_std) , why a_std is not 1 for example ? — Mohammed almalki
– Mohammed almalki, Commented Aug 8, 2024 at 15:52
@Mohammedalmalki - The order must remain fixed. Assume that the order should match the desired outcome for this question. — gwydion93
– gwydion93, Commented Aug 8, 2024 at 16:36
Desired outcome. Essentially: order = {"norm":1, "std":2,"min":3,"max":4,"flag":5} — gwydion93
– gwydion93, Commented Aug 8, 2024 at 16:45
Stack Overflow is meant for specific questions, so "suggestions" is too broad. What exactly do you need help with? Like to start, do you realize that the while loop is unnecessary, set is not what you want, and i + 1 has no effect? Check out How to Ask and you can edit to clarify if needed. — wjandrea
– wjandrea, Commented Aug 8, 2024 at 16:47

Scott Hunter · Accepted Answer · 2024-08-08 17:28:29Z

2

This will do the parsing you want; you can then assign the items in parsed_lists as you wish.

parsed_lists = {'a':[], 'b':[], 'c':[]}
for x in my_list:
    v = parsed_lists[x[0]]
    v.append([len(v)+1,x])

which results in:

{'a': [[1, 'a_norm'], [2, 'a_std'], [3, 'a_min'], [4, 'a_max'], [5, 'a_flag']], 
 'b': [[1, 'b_norm'], [2, 'b_std'], [3, 'b_min'], [4, 'b_max'], [5, 'b_flag']], 
 'c': [[1, 'c_norm'], [2, 'c_std'], [3, 'c_min'], [4, 'c_max'], [5, 'c_flag']]}

edited Aug 8, 2024 at 17:28

answered Aug 8, 2024 at 15:51

Scott Hunter

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1 Comment

gwydion93 Over a year ago

Great answer. I went with this because it was the most succinct. Appreciate all the answers and feedback.

chepner · Accepted Answer · 2024-08-08 16:32:23Z

1

You can use itertools.groupby to group your original list into subsequences based on the first letter of each list element.

>>> from itertools import groupby
>>> from operator import itemgetter
>>> f = itemgetter(0)
>>> my_list = ['a_norm', 'a_std', 'a_min', 'a_max', 'a_flag', 'b_norm', 'b_std', 'b_min', 'b_max', 'b_flag', 'c_norm', 'c_std', 'c_min', 'c_max', 'c_flag']
>>> d = {k: list(map(list, enumerate(v, start=1))) for k, v in groupby(sorted(my_list, key=f), f)}
>>> d['a']
[[1, 'a_norm'], [2, 'a_std'], [3, 'a_min'], [4, 'a_max'], [5, 'a_flag']]

answered Aug 8, 2024 at 16:32

chepner

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Comments

wjandrea · Accepted Answer · 2024-08-08 16:49:03Z

this code does your jobs that you want,

but I do not know depends on what you order the values like (a_norm , a_std) , why a_std is not 1 for example ?

but this is the code:

my_list = ['a_norm', 'a_std', 'a_min', 'a_max', 'a_flag', 'b_norm', 'b_std', 'b_min', 'b_max', 'b_flag', 'c_norm', 'c_std', 'c_min', 'c_max', 'c_flag']

letters = {}

order = {"norm":1,
         "std":2,
         "min":3,
         "max":4,
         "flag":5}

for i in my_list:
    letter = i.split("_")[0]
    value = i.split("_")[1]

    to_append = [order.get(value), i]

    if letters.get(letter):
        letters.get(letter).append(to_append)
    else:
        letters.update({letter : [to_append]})

print(letters)

a_list = letters.get("a")
b_list = letters.get("b")
c_list = letters.get("c")

print(a_list)
print(b_list)
print(c_list)

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