CODEWITHSUNDEEP
pythonpandasdataframe
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Reputation: 5367

How to add columns to an empty pandas dataframe?

I have an empty dataframe.

df=pd.DataFrame(columns=['a'])

for some reason I want to generate df2, another empty dataframe, with two columns 'a' and 'b'.

If I do 

df.columns=df.columns+'b'

it does not work (I get the columns renamed to 'ab') and neither does the following 

df.columns=df.columns.tolist()+['b']

How to add a separate column 'b' to df, and df.emtpy keep on being True?

Using .loc is also not possible

   df.loc[:,'b']=None

as it returns 

  Cannot set dataframe with no defined index and a scalar

Upvotes: 40

Views: 76205

Answers (6)

Pramod B R
Pramod B R

Reputation: 662

You can simply use the following syntax

import pandas as pd
df = pd.DataFrame(columns=['A', 'B', 'C'])
df[['D', 'E', 'F']] = None
print(df)

This creates an empty dataframe with columns from 'A' to 'F' with below result

 >>Empty DataFrame
 >>Columns: [A, B, C, D, E, F]
 >>Index: []

Upvotes: 0

jpp
jpp

Reputation: 164853

This is one way:

df2 = df.join(pd.DataFrame(columns=['b']))

The advantage of this method is you can add an arbitrary number of columns without explicit loops.

In addition, this satisfies your requirement of df.empty evaluating to True if no data exists.

Upvotes: 6

BENY
BENY

Reputation: 323396

You can use concat:

df=pd.DataFrame(columns=['a'])
df
Out[568]: 
Empty DataFrame
Columns: [a]
Index: []

df2=pd.DataFrame(columns=['b', 'c', 'd'])
pd.concat([df,df2])
Out[571]: 
Empty DataFrame
Columns: [a, b, c, d]
Index: []

Upvotes: 4

Ben.T
Ben.T

Reputation: 29635

If you just do df['b'] = None then df.empty is still True and df is:

Empty DataFrame
Columns: [a, b]
Index: []

EDIT: To create an empty df2 from the columns of df and adding new columns, you can do:

df2 = pd.DataFrame(columns = df.columns.tolist() + ['b', 'c', 'd'])

Upvotes: 21

Sumit Jha
Sumit Jha

Reputation: 1691

Here are few ways to add an empty column to an empty dataframe:

df=pd.DataFrame(columns=['a'])
df['b'] = None
df = df.assign(c=None)
df = df.assign(d=df['a'])
df['e'] = pd.Series(index=df.index)   
df = pd.concat([df,pd.DataFrame(columns=list('f'))])
print(df)

Output:

Empty DataFrame
Columns: [a, b, c, d, e, f]
Index: []

I hope it helps.

Upvotes: 55

ALollz
ALollz

Reputation: 59579

If you want to add multiple columns at the same time you can also reindex.

new_cols = ['c', 'd', 'e', 'f', 'g']
df2 = df.reindex(df.columns.union(new_cols), axis=1)

#Empty DataFrame
#Columns: [a, c, d, e, f, g]
#Index: []

Upvotes: 10

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