Modify Columns

Problem

DataFrame employees +-------------+--------+ | Column Name | Type | +-------------+--------+ | name | object | | salary | int | +-------------+--------+

A company intends to give its employees a pay rise.

Write a solution to modify the salary column by multiplying each salary by 2.

The result format is in the following example.

Examples

Example 1

Input: DataFrame employees
+---------+--------+
| name    | salary |
+---------+--------+
| Jack    | 19666  |
| Piper   | 74754  |
| Mia     | 62509  |
| Ulysses | 54866  |
+---------+--------+
Output: +---------+--------+
| name    | salary |
+---------+--------+
| Jack    | 39332  |
| Piper   | 149508 |
| Mia     | 125018 |
| Ulysses | 109732 |
+---------+--------+
Explanation: Every salary has been doubled.

## Solution

### Method 1 – Direct Column Update

#### Intuition
The simplest way to double every salary is to directly update the `salary` column by multiplying its value by 2. This can be done efficiently in SQL or pandas with a single statement.

#### Approach
1. Use an UPDATE statement in SQL to multiply the `salary` column by 2 for all rows.
2. In pandas, use vectorized assignment to update the column in one line.
3. The operation is performed in-place, so no extra space is needed except for the result.

#### Code

{{< code_tabs >}}
##### MySQL
```sql
UPDATE employees
SET salary = salary * 2;

PostgreSQL

UPDATE employees
SET salary = salary * 2;

Python (pandas)

def modify_salary(employees: pd.DataFrame) -> pd.DataFrame:
    employees['salary'] = employees['salary'] * 2
    return employees

Complexity

• ⏰ Time complexity: O(n) — Each row's salary is updated once.
• 🧺 Space complexity: O(1) — The update is in-place, no extra space is used.