Create Pandas DataFrame from a Numpy Array

Pandas dataframes are quite versatile when it comes to manipulating 2D tabular data in python. And often it can be quite useful to convert a numpy array to a pandas dataframe for manipulating or transforming data. In this tutorial, we’ll look at how to create a pandas dataframe from a numpy array.

Using the pandas.DataFrame() function

To create a pandas dataframe from a numpy array, pass the numpy array as an argument to the pandas.DataFrame() function. You can also pass the index and column labels for the dataframe. The following is the syntax:

df = pandas.DataFrame(data=arr, index=None, columns=None)

Examples

Let’s look at a few examples to better understand the usage of the pandas.DataFrame() function for creating dataframes from numpy arrays.

1. 2D numpy array to a pandas dataframe

Let’s create a dataframe by passing a numpy array to the pandas.DataFrame() function and keeping other parameters as default.

import numpy as np
import pandas as pd

# sample numpy array
arr = np.array([[70, 90, 80], [68, 80, 93]])
# convert to pandas dataframe with default parameters
df = pd.DataFrame(arr)

# print
print("Numpy array:\n", arr)
print("\nPandas dataframe:\n", df)

Output:

Numpy array:
 [[70 90 80]
 [68 80 93]]

Pandas dataframe:
     0   1   2
0  70  90  80
1  68  80  93

In the above example, the dataframe df is created from the numpy array arr. Note that since we did not pass the index and column labels, the created dataframe used the default RangeIndex for them.

Let’s pass custom index and column labels to the dataframe being created.

import numpy as np
import pandas as pd

# sample numpy array
arr = np.array([[70, 90, 80], [68, 80, 93]])
# convert to pandas dataframe with custom index and column names
df = pd.DataFrame(arr, columns=['History', 'Physics', 'Math'], index=['Sam', 'Emma'])

# print
print("Numpy array:\n", arr)
print("\nPandas dataframe:\n", df)

Output:

Numpy array:
 [[70 90 80]
 [68 80 93]]

Pandas dataframe:
       History  Physics  Math
Sam        70       90    80
Emma       68       80    93

Here, the index labels and column names are passed to the arguments index and columns respectively. From the labels, we can assume that the dataframe stores the test scores of students Sam and Emma in the subjects History, Physics and Math.

2. 1D numpy array to a pandas dataframe

Passing a one-dimensional numpy array to the pandas.DataFrame() function will result in a pandas dataframe with one column.

import numpy as np
import pandas as pd

# sample numpy array
arr = np.array([10, 20, 30, 40])
# convert to pandas dataframe
df = pd.DataFrame(arr)

# print
print("Numpy array:\n", arr)
print("\nPandas dataframe:\n", df)

Output:

Numpy array:
 [10 20 30 40]

Pandas dataframe:
     0
0  10
1  20
2  30
3  40

Fore more on the pandas.DataFrame() function, refer to its official documentation.

Additional Note

Pandas dataframes are objects used to store two-dimensional tabular data. If you try to create a pandas dataframe from a numpy array with more than 2 dimensions, you’ll get an error. See the example below.

import numpy as np
import pandas as pd

# sample numpy array
arr = np.random.randint(1,5,(3,3,2))
print("Numpy array:\n", arr)
# convert to pandas dataframe
df = pd.DataFrame(arr)
print("\nPandas dataframe:\n", df)

Output:

Numpy array:
 [[[4 4]
  [2 2]
  [2 2]]

 [[2 2]
  [4 4]
  [1 3]]

 [[3 4]
  [4 1]
  [2 2]]]
---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-12-8c5dce07516e> in <module>
      6 print("Numpy array:\n", arr)
      7 # convert to pandas dataframe
----> 8 df = pd.DataFrame(arr)
      9 print("\nPandas dataframe:\n", df)

~\anaconda3\lib\site-packages\pandas\core\internals\construction.py in prep_ndarray(values, copy)
    293         values = values.reshape((values.shape[0], 1))
    294     elif values.ndim != 2:
--> 295         raise ValueError("Must pass 2-d input")
    296 
    297     return values

ValueError: Must pass 2-d input

* Some lines in the above error message have been skipped to shorten the output shown.

With this, we come to the end of this tutorial. The code examples and results presented in this tutorial have been implemented in a Jupyter Notebook with a python (version 3.8.3) kernel having numpy version 1.18.5 and pandas version 1.0.5