How do I use a loop statement to change specific values in a dictionary given an if statement?-CodePudding

If I have a dictionary with each key having a list of values for example:

my_dict={'key1':[1, 6, 7, -9], 'key2':[2, 5, 10, -5,], 'key3':[-8, 1, -2, 6]}

And I want to create a loop statement to go through each value within the lists and change the value within my dictionary to 0 for each negative value. I can create a loop statement to go through each value and check if the value is negative but I can't figure out how to amend the dictionary directly:

for keys, values in my_dict.items():
    for value in values:
        if value < 0:
            value=0

How to I alter that last line (or do I have to change more lines) to be able to amend my dictionary directly to replace the negative values with 0?

Thanks in advance

CodePudding user response：

One approach is to iterate over the .items of the dictionary and override each value directly using enumerate to keep track of the indices:

my_dict={'key1':[1, 6, 7, -9], 'key2':[2, 5, 10, -5,], 'key3':[-8, 1, -2, 6]}

for key, value in my_dict.items():
    for i, val in enumerate(value):
        value[i] = 0 if val < 0 else val

print(my_dict)

Output

{'key1': [1, 6, 7, 0], 'key2': [2, 5, 10, 0], 'key3': [0, 1, 0, 6]}

Alternative using the slicing operator and a list comprehension:

for key, value in my_dict.items():
    value[:] = [0 if val < 0 else val for val in value]

Some other useful resources:

Looping Techniques, discusses pythonic approaches to looping
Python names and values for understanding how variables work in Python
Slice assignment some light on how the second approach works

CodePudding user response：

Using max in a nested comprehension:

my_dict = {k: [max(0, v) for v in vals] for k, vals in my_dict.items()}