Adding and Dropping Columns

Adding columns

There are various ways you can add new columns to a DaraFrame.

Assign the same value to every row

import pandas as pd​df = pd.DataFrame({"A": [1, 2, 3]})df["B"] = 10print(df)

Output:

   A   B0  1  101  2  102  3  10

Assigning a list or array

• Assign different values per row (length must match number of rows).

df["C"] = [100, 200, 300]print(df)

Output:

   A   B    C0  1  10  1001  2  10  2002  3  10  300

Using calculations on existing columns

• New columns can be derived from existing ones.
• Changes the original DataFrame.

df["D"] = df["A"] + df["C"]print(df)

Output:

   A   B    C    D0  1  10  100  1011  2  10  200  2022  3  10  300  303

Using .assign()

• Creates a new column (or multiple) without modifying the original.
• Can also be chained together.

df = df.assign(E=df["D"] * 2)print(df)

Using .insert()

• Insert a column at a specific position.

 # insert at index 1df.insert(1, "F", [7, 8, 9]) print(df)

Output:

   A  F   B    C    D   E0  1  7  10  100  101  2021  2  8  10  200  202  4042  3  9  10  300  303  606

Dropping columns

There are also various ways you can remove columns from a DataFrame.

Using .drop()

• Drops columns by name.

df.drop("B", axis=1, inplace=True)  # axis=1 for columns

Drop multiple columns::

df.drop(["C", "D"], axis=1, inplace=True)

Key parameters:

• axis=1 → columns
• axis=0 → rows (default)
• inplace=True → modify the DataFrame directly

Using del

• Deletes a single column.

del df["F"]

Using .pop()

• Removes a column and returns it.

popped_column = df.pop("E")​print(popped_column)