Converting numpy array into dataframe column?

Question

How do I convert a numpy array into a dataframe column. Let's say I have created an empty dataframe, df, and I loop through code to create 5 numpy arrays. Each iteration of my for loop, I want to convert the numpy array I have created in that iteration into a column in my dataframe. Just to clarify, I do not want to create a new dataframe every iteration of my loop, I only want to add a column to the existing one. The code I have below is sketchy and not syntactically correct, but illustrates my point.

df = pd.dataframe()
for i in range(5):
   arr = create_numpy_arr(blah) # creates a numpy array
   df[i] = # convert arr to df column

user1596433 · Accepted Answer · 2019-10-19 09:07:31Z

26

This is the simplest way:

df['column_name']=pd.Series(arr)

answered Oct 19, 2019 at 9:07

user1596433

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Julio Cezar Silva · Accepted Answer · 2019-04-13 20:51:01Z

8

Since you want to create a column and not an entire DataFrame from your array, you could do

import pandas as pd
import numpy as np

column_series = pd.Series(np.array([0, 1, 2, 3]))

To assign that column to an existing DataFrame:

df = df.assign(column_name=column_series)

The above will add a column named column_name into df.

If, instead, you don't have any DataFrame to assign those values to, you can pass a dict to the constructor to create a named column from your numpy array:

df = pd.DataFrame({ 'column_name': np.array([0, 1, 2, 3]) })

answered Apr 13, 2019 at 20:51

Julio Cezar Silva

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user2047399 · Accepted Answer · 2017-06-08 00:13:18Z

1

That will work

import pandas as pd
import numpy as np

df = pd.DataFrame()

for i in range(5):
    arr = np.random.rand(10)
    df[i] = arr

Maybe a simpler way is to use the vectorization

arr = np.random.rand(10, 5)
df = pd.DataFrame(arr)

answered Jun 8, 2017 at 0:13

user2047399

Comments

TPArrow · Accepted Answer · 2023-03-24 18:46:32Z

1

Another way if you have a 2d array:

pd.DataFrame(np.matrix.transpose(array))

answered Mar 24, 2023 at 18:46

TPArrow

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