Methods to search and replace values in nested lists

Question

I'd like to search and replace values in a list of of list. I've cobbled together answers to:

My current code works however I feel that it's more convoluted then it needs to be. Is there a more elegant way of doing this?

# Create test data- a list of lists which each contain 2 items
numbers = list(range(10))
list_of_lists = [numbers[i:i+2] for i in range(0, len(numbers), 2)]

# Flatten the list of lists
flat_list = [item for sublist in list_of_lists for item in sublist]
# Search for and replace values
modified_list = [-1 if e > 5 else e for e in flat_list]
# Regroup into a list of lists
regrouped_list_of_lists = [modified_list[i:i+2] for i in range(0, len(modified_list), 2)]

This is probably the most Pythonic way of doing it. If it works and is readable, don't fix it! — TheLazyScripter, Sep 11 '16 at 23:35
@TheLazyScripter *If it works and is readable, don't fix it* Nah, not in this case. — Moses Koledoye, Sep 11 '16 at 23:44

score 2 · Answer 1 · answered Sep 11 '16 at 23:36

2

You're already using list comprehensions, just combine them:

replaced_list_of_lists = [
            [-1 if e > 5 else e for e in inner_list]
                for inner_list in list_of_lists
        ]

answered Sep 11 '16 at 23:36

J Earls

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I'm not sure this is a good answer. List comprehension add already much to the readability, and combining them doesn't help much. – Antoine Sep 11 '16 at 23:37
Well this definitely removes some of the code so why not, but I personally try to avoid heavy use of list comprehension. – Antoine Sep 11 '16 at 23:40
@AntoineBolvy however, the original solution of flatting / replacing / recombing only works if you know exactly the format of the original list. If you want a general solution, you need either list comprehensions or nested for loops. – J Earls Sep 11 '16 at 23:42
Yeah of course, although it is useful to not forget that nested list comprehensions *are* nested for loops ;) – Antoine Sep 11 '16 at 23:54

score 2 · Accepted Answer · answered Sep 11 '16 at 23:37

Make the replacements in the sublists in a nested list comprehension without having to flatten and regroup:

numbers = list(range(10))
list_of_lists = [numbers[i:i+2] for i in range(0, len(numbers), 2)]
# here
list_of_lists = [[-1 if e > 5 else e for e in sublist] for sublist in list_of_lists]

Methods to search and replace values in nested lists

2 Answers2