List of list (multi dimensional array) into pandas Data Frame column

Question

Having a multi dimensional array, and I want to introduced as a column into a df.

import pandas as pd
import numpy as np

x = np.array([[1, 2, 3], [4, 5, 6]], np.int32)
df = pd.DataFrame(['A', 'B'], columns=['First'])

Initial df:

  First 
0     A 
1     B

Final output should be:

  First  Second  
0     A   [1,2,3]
1     B   [4,5,6]

The final obj is to upload the table into a data base, and I understand is not the best way to keep records. If you have any recommendations are more than welcome.

Thanks.

df['second'] = [v for v in x] or df['second'] = list(x)... — Quang Hoang
– Quang Hoang, Commented Nov 27, 2019 at 16:58

yatu · Accepted Answer · 2019-11-27 17:09:37Z

3

You can directly assign the array x by unpacking its rows into a list:

df.assign(second=[*x])

   First  second
0     A  [1, 2, 3]
1     B  [4, 5, 6]

Note that, as mentioned in the comments this is the same as:

df.assign(second=list(x))

edited Nov 27, 2019 at 17:09

answered Nov 27, 2019 at 17:02

yatu

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12 Comments

yatu Over a year ago

Let me add some details... @yuca

Yuca Over a year ago

so is this a short hand for list comprehension? I get that you're calling a list over the contents of x, just wondering about the more technical detaiils

anky Over a year ago

@Yuca same as df.assign(k=list(x))

yatu Over a year ago

Yes exactly @anky

anky Over a year ago

@AlexSB except if you want to chain other operations (assign lets you do that), since assign() returns a copy whereas df[var]=.. is an inplace operation

|

ansev · Accepted Answer · 2019-11-27 17:01:29Z

2

Use:

df['Second']=x.tolist()
print(df)

  First     Second
0     A  [1, 2, 3]
1     B  [4, 5, 6]

answered Nov 27, 2019 at 17:01

ansev

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Comments

BENY · Accepted Answer · 2019-11-27 17:05:38Z

1

Even though this will extend the length of table , I still recommend explode it , after groupby you can always convert it back.

Object data type in single columns will disable most of db query functions and pandas functions

df.assign(list=x.tolist()).explode('list')
Out[6]: 
  First list
0     A    1
0     A    2
0     A    3
1     B    4
1     B    5
1     B    6

answered Nov 27, 2019 at 17:05

BENY

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Comments

Khakhar Shyam · Accepted Answer · 2019-11-27 17:17:30Z

1

 import pandas as pd
 import numpy as np

 x = np.array([[1, 2, 3], [4, 5, 6]], np.int32)
 df = pd.DataFrame(['A', 'B'], columns=['First'])
 df['second'] = [i for i in x] or df['second'] = list(x)
 print(df)

edited Nov 27, 2019 at 17:17

answered Nov 27, 2019 at 17:02

Khakhar Shyam

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