How to replace elements in a list using dictionary lookup

Question

Given this list

my_lst = ['LAC', 'HOU', '03/03 06:11 PM', '2.13', '1.80', '03/03 03:42 PM']

I want to change its 0th and 1st values according to the dictionary value:

def translate(my_lst):
    subs = {
        "Houston": "HOU", 
        "L.A. Clippers": "LAC",

    }

so the list becomes:

['L.A. Clippers', 'Houston', '03/03 06:11 PM', '2.13', '1.80', '03/03 03:42 PM']

Asked By: nutship

||

Source

Answer 1

If all values are unique then you should reverse the dict first to get an efficient solution:

>>> subs = {
...         "Houston": "HOU", 
...         "L.A. Clippers": "LAC",
... 
...     }
>>> rev_subs = { v:k for k,v in subs.iteritems()}
>>> [rev_subs.get(item,item)  for item in my_lst]
['L.A. Clippers', 'Houston', '03/03 06:11 PM', '2.13', '1.80', '03/03 03:42 PM']

If you’re only trying to updated selected indexes, then try:

indexes = [0, 1]
for ind in indexes:
    val =  my_lst[ind]
    my_lst[ind] = rev_subs.get(val, val)

Answered By: Ashwini Chaudhary

Answer 2

If the values are unique, then you can flip the dictionary:

subs = {v:k for k, v in subs.iteritems()}

Then you can use .get() to get the value from a dictionary, along with a second parameter incase the key is not in the dictionary:

print map(subs.get, my_lst, my_lst)

Prints:

['L.A. Clippers', 'Houston', '03/03 06:11 PM', '2.13', '1.80', '03/03 03:42 PM']

Answered By: TerryA

Answer 3

Reverse the dict, then just apply the lookup to the first 2 elements of your list:

subs = {
    "Houston": "HOU", 
    "L.A. Clippers": "LAC",

}

my_lst = ['LAC', 'HOU', '03/03 06:11 PM', '2.13', '1.80', '03/03 03:42 PM']
my_lst[:2] = map(dict(zip(subs.values(), subs)).get, my_lst[:2])
print my_lst

Answered By: Jon Clements

Answer 4

if you want something shorter, you can exploit the series function in pandas

import pandas as pd
A = ['A','B','A','C','D'] #list we want to replace with a dictionary lookup
B = {'A':1,'B':2,'C':3,'D':4} #dictionary lookup, dict values in B will be mapped to entries in A
C = (pd.Series(A)).map(B) #convert the list to a pandas series temporarily before mapping
D = list(C) # we transform the mapped values (a series object) back to a list
# entries in D = [1,2,1,3,4]

Answered By: Chidi

Answer 5

This is a one-line in pandas ….

df['A'].replace(dict(zip(
        ['SERVICIOS', 'ECON?MICO', 'ECONOMICO', 'EN ESPECIE'],
        ['servicios', 'economico', 'economico', 'en especie'])
                       ),regex=True)

Answered By: Rainer

Answer 6

Thanks @ashwini-chaudhary
https://stackoverflow.com/users/846892/ashwini-chaudhary
Update for Python3, use items() instead of iteritems()

rev_subs = { v:k for k,v in subs.items()}

Answered By: DSBLR

How to replace elements in a list using dictionary lookup

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