CODEWITHSUNDEEP
pythonpython-3.xlist
VitaPepe
VitaPepe

Reputation: 45

Replacing elements in list with values from dictionary

I want to replace strings in a list with values from dictionary. However, for some logical reason which is not logical to me (obviously), length of list changes after replacement.

genre_list = ['action, drama, thriller', 'crime, romance, adventure']

list_new = []

categories_ids = {'action': '18',
                  'drama': '13',
                  'thriller': '11',
                  'romance': '1',
                  'adventure': '8',
                  'crime': '3'
                  }

print(len(genre_list)) # length before

for z in genre_list:
    for a, b in categories_ids.items():
        if a in z:
            list_temp = z.replace(z, b)
            list_new.append(list_temp)

print(len(list_new)) # length after

What am I missing here? Thanks in advance.

Upvotes: 1

Views: 103

Answers (4)

Sathish
Sathish

Reputation: 44

Each list element contains more than 1 keys which is reason you end up with more elements in the new list. This can be handled as given the code below.

for z in genre_list:
    key_words=''
    for key in z.split(','):
        if key.strip() in categories_ids:
            key_words += categories_ids[key.strip()] +','
    list_new.append(key_words[:-1])

Now both the lists will have same length as given below.

2 ['action, drama, thriller', 'crime, romance, adventure']

2 ['18,13,11', '3,1,8']

Upvotes: 1

kederrac
kederrac

Reputation: 17322

you are adding new elements to your new_list if a key from your dict is in one string from genre_list but the genre_list has in one string multiple keys from your dict so you end to have multiple strings/elements in your new_list

you can use a regular expression with list comprehension:

import re

genre_list = ['action, drama, thriller', 'crime, romance, adventure']
pattern = '|'.join(categories_ids)
def replace(gr):
    return categories_ids[gr.group()]

list_new = [re.sub(pattern, replace, t) for t in genre_list]
# ['18, 13, 11', '3, 1, 8']

Upvotes: 1

Gabio
Gabio

Reputation: 9494

You append to list_new each element from categories that appears in each element of genre_list - the first 3 keys appears in the first element of genre_list and the 3 other keys appears in the second element of genre_list - so in list_new will be 6 elements in total.

Try instead:

genre_list = ['action, drama, thriller', 'crime, romance, adventure'] 

list_new = []                                                         

categories_ids = {'action': '18',                                     
                  'drama': '13',                                      
                  'thriller': '11',                                   
                  'romance': '1',                                     
                  'adventure': '8',                                   
                  'crime': '3'                                        
                  }                                                   

for z in genre_list:                                                  
    for a, b in categories_ids.items():                               
        z = z.replace(a, b)                                           
    list_new.append(z) # here is the difference - one append per element in genre_list                                               

print(list_new) # output:['18, 13, 11', '3, 1, 8']

Upvotes: 2

Shubham Sharma
Shubham Sharma

Reputation: 71689

Use:

def func(s):
    return ", ".join(categories_ids[w] for w in s.split(", "))

list_new = list(map(func, genre_list))
print(list_new)

This prints:

['18, 13, 11', '3, 1, 8']

Upvotes: 1

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