Add one row to pandas DataFrame


Question

I understand that pandas is designed to load fully populated DataFrame but I need to create an empty DataFrame then add rows, one by one. What is the best way to do this ?

I successfully created an empty DataFrame with :

res = DataFrame(columns=('lib', 'qty1', 'qty2'))

Then I can add a new row and fill a field with :

res = res.set_value(len(res), 'qty1', 10.0)

It works but seems very odd :-/ (it fails for adding string value)

How can I add a new row to my DataFrame (with different columns type) ?

1
674
1/3/2019 3:25:19 PM

Accepted Answer

>>> import pandas as pd
>>> from numpy.random import randint

>>> df = pd.DataFrame(columns=['lib', 'qty1', 'qty2'])
>>> for i in range(5):
>>>     df.loc[i] = ['name' + str(i)] + list(randint(10, size=2))

>>> df
     lib qty1 qty2
0  name0    3    3
1  name1    2    4
2  name2    2    8
3  name3    2    1
4  name4    9    6
436
7/10/2019 7:28:32 PM

In case you can get all data for the data frame upfront, there is a much faster approach than appending to a data frame:

  1. Create a list of dictionaries in which each dictionary corresponds to an input data row.
  2. Create a data frame from this list.

I had a similar task for which appending to a data frame row by row took 30 min, and creating a data frame from a list of dictionaries completed within seconds.

rows_list = []
for row in input_rows:

        dict1 = {}
        # get input row in dictionary format
        # key = col_name
        dict1.update(blah..) 

        rows_list.append(dict1)

df = pd.DataFrame(rows_list)               

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