Insert cells in empty Pandas DataFrame

Question

I need to store some values in an empty Pandas Dataframe. Something like that :

      | col1  col2  col3
------------------------
row1  |  v1    v2    v3
row2  |  v4    v5    v6
row3  |  v7    v8    v9

I get cells from other sources ex: (row2, col3, v6) and I don't know in advance how many rows and how many columns I will have.

I tried to fill my DataFrame this way, but it's not working :

import pandas as pd

df = pd.DataFrame()

df["col1"] = ""
df["col2"] = ""
df["col3"] = ""

df["col1"].loc["row1"] = "v1"
df["col2"].loc["row2"] = "v4"
df["col3"].loc["row3"] = "v9"
# ...

When I want to display DataFrame,

print(df)

it shows as an empty DataFrame.

Empty DataFrame
Columns: [col1, col2, col3]
Index: []

Out of curiosity, I tried

print(df["col1"])

and I get :

row1    v1
row2    v4
row3    v7
Name: col1, dtype: object

And

print(df.loc["row1"])

returns a KeyError exception.

Well, I guess I have an index problem but I don't know how to address it and I cannot use df.set_index after first insertion since I have other constraints.

I tried this too:

df = pd.DataFrame(columns=("some_name",))
df.set_index("some_name", inplace=True)

but it failed too.

Any idea ? I think I just need to set an empty index before starting to insert data, but I don't know how.

Answer 1

This way you can add values using the pd.loc() method: import pandas as pd df = pd.DataFrame()

df["col1"] = ""
df["col2"] = ""
df["col3"] = ""

df.loc["row1", "col1"] = "v1"
df.loc["row2", "col2"] = "v4"
df.loc["row3", "col3"] = "v9"

Producing the following output: