Merging two string lists in pandas

Question

I have a dataframe with two series x and y. I want to merge them to create a new series: tag, but I'm not able to achieve the expected output. I've tried:

df['tag'] = df['x'] + df['y']

I've looked everywhere and haven't been able to find a solution to the problem.

Current output:

x                               y           tag
['fast food', 'american']   ['chicken'] ['fast food', 'american']['chicken']

Expected output:

x                               y           tag
['fast food', 'american']   ['chicken'] ['fast food', 'american', 'chicken']

df.to_dict()

{'x': "['fast food', 'american']",
 'y': "['chicken']"}

BENY · Accepted Answer · 2019-07-09 01:15:07Z

2

I do not think that is list , so you may convert it into list , them you can sum

import ast
df.x = df.x.apply(ast.literal_eval)
df.y = df.y.apply(ast.literal_eval)

df['tag'] = df['x'] + df['y']

More info

df=pd.DataFrame()
df['y']=["['chicken']"]
df['x']=["['fast food', 'american']"]
df.applymap(type)
Out[295]: 
               y              x
0  <class 'str'>  <class 'str'>


df.x = df.x.apply(ast.literal_eval)
df.y = df.y.apply(ast.literal_eval)
df.applymap(type)
Out[297]: 
                y               x
0  <class 'list'>  <class 'list'>

edited Jul 9, 2019 at 1:15

answered Jul 9, 2019 at 1:07

BENY

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3 Comments

Pepe Over a year ago

With this solution I must have a string list inside a list, how can I do that?

BENY Over a year ago

@Pepe in the mean time . convert it by df=df.astype(str), then using above method

BENY Over a year ago

@Pepe did you try my method , ? df.x = df.x.apply(ast.literal_eval) df.y = df.y.apply(ast.literal_eval) df['tag'] = df['x'] + df['y'], this solved the problem

Chris · Accepted Answer · 2019-07-09 02:28:13Z

0

Another way is to use re.findall:

import re

df.applymap(lambda x:re.findall("'(.+?)'", x)).sum(1)

which will return a list of strs:

                           x            y                             tag
0  ['fast food', 'american']  ['chicken']  [fast food, american, chicken]

answered Jul 9, 2019 at 2:28

Chris

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Comments

Gustavo Gradvohl · Accepted Answer · 2019-07-09 02:39:06Z

0

You can unpack the list and use apply to create your new column.

answered Jul 9, 2019 at 2:39

Gustavo Gradvohl

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Comments

JKC · Accepted Answer · 2019-07-10 03:40:27Z

-1

UPDATED

Try this :

df=pd.DataFrame()
df['X']=[["chicken"]]
df['Y']=[["fast food","American"]]
df['tag']=df['X']+df['Y']

edited Jul 10, 2019 at 3:40

answered Jul 9, 2019 at 1:15

JKC

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2 Comments

Pepe Over a year ago

returns the same result I posted.

JKC Over a year ago

Apologies @Pepe . Updated the answer. Check it out

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