add a column to the dataframe using a loop in python pandas

Question

I've a sample dataframe

id      city
1       Florida
2       Atlanta
3       Manhattan
4       Amsterdam
5       Newyork

I've a function

def my_function(x):
    y = x[::-1]
    return y

How can I make a for loop that uses city column and inserts the reversed string in a column one by one which results the below?

id      city       reversed_string
 1      Florida       adirolF
 2      Atlanta       atnaltA
 3      Manhattan     nattahnaM
 4      Amsterdam     madretsmA
 5      Newyork       kroyweN

gofvonx · Accepted Answer · 2021-04-17 17:50:41Z

2

You can use the fact that a string in Python is an iterable. Note that you do not need apply.

df['reversed_string'] = df.city.str[::-1]

answered Apr 17, 2021 at 17:50

gofvonx

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3 Comments

astroboy1 Over a year ago

thanks @gofvonx. I'm just looking for how to use a function iteratively. The objective is not to reverse the string, but how to use a function.

gofvonx Over a year ago

@astroboy1 Thanks for clarifying. I'd still make the point that you can very often get away with not using apply at all (which usually is less efficient and not what should be understood when people talk about "vectorizing").

Edwin Cheong Over a year ago

I see i will keep in mind in the future, it's just apply was one of the more common use case when i am using pandas, thanks for the advice

Edwin Cheong · Accepted Answer · 2021-04-17 17:55:18Z

1

Simple just use an apply without a for loop

df['reversed_string'] = df['city'].apply(lambda x: x[::-1])

If you want to use it with a function

def reverse_string(string):
  return string[::-1]

df['revered_string'] = df['city'].apply(reverse_string)

edited Apr 17, 2021 at 17:55

answered Apr 17, 2021 at 17:51

Edwin Cheong

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3 Comments

gofvonx Over a year ago

I don't think that apply is necessary here.

anky Over a year ago

Apply might be necessary, we dont know what the actual usecase/how complicated the function is, upvoted both answer..!!

Edwin Cheong Over a year ago

In hindsight, i'm just suggesting the one possible solutions you can take

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