How do I create a new column in a DataFrame?

You can create a new column by using direct assignment, such as `df['bonus'] = df['salary'] * 2`.

What methods can I use to create a new column in pandas?

You can use direct assignment, the `assign()` method, or the `apply()` method with a lambda function.

What is the time complexity of adding a new column in pandas?

The time complexity is O(n), where n is the number of rows in the DataFrame.

How do I calculate a column based on another column in pandas?

You can calculate a column by using simple arithmetic operations or functions, like `df['new_column'] = df['existing_column'] * 2`.

What are some common mistakes when creating new columns in pandas?

Common mistakes include incorrect syntax, not handling missing values, or performing calculations incorrectly.

#2881

Easy

auto_awesomeCreate a New Column core interview pattern

LeetCode 题解工作台

创建新列

题目描述

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

一家公司计划为员工提供奖金。

编写一个解决方案，创建一个名为 bonus 的新列，其中包含 salary 值的两倍。

返回结果格式如下示例所示。

示例 1:

输入：
DataFrame employees
+---------+--------+
| name    | salary |
+---------+--------+
| Piper   | 4548   |
| Grace   | 28150  |
| Georgia | 1103   |
| Willow  | 6593   |
| Finn    | 74576  |
| Thomas  | 24433  |
+---------+--------+
输出：
+---------+--------+--------+
| name    | salary | bonus  |
+---------+--------+--------+
| Piper   | 4548   | 9096   |
| Grace   | 28150  | 56300  |
| Georgia | 1103   | 2206   |
| Willow  |  593   | 13186  |
| Finn    | 74576  | 149152 |
| Thomas  | 24433  | 48866  |
+---------+--------+--------+
解释：
通过将 salary 列中的值加倍创建了一个新的 bonus 列。

lightbulb

解题思路

方法一：直接计算

我们可以直接计算 salary 的两倍，然后将结果存入 bonus 列。

时间复杂度 $O(1)$ ，空间复杂度 $O(1)$ 。

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import pandas as pd


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

speed

复杂度分析

指标	值
时间	Depends on the final approach
空间	Depends on the final approach

psychology

面试官常问的追问

外企场景

question_mark
The candidate uses direct assignment to create the new column.
question_mark
The candidate understands DataFrame manipulation with methods like `assign()` or `apply()`.
question_mark
The candidate demonstrates knowledge of computational complexity in the context of DataFrame operations.

warning

常见陷阱

外企场景

error
Incorrectly assigning the new column without ensuring it calculates the correct value.
error
Not handling edge cases such as missing or negative salary values.
error
Misunderstanding the DataFrame assignment syntax, leading to errors or incorrect results.

swap_horiz

进阶变体

外企场景

arrow_right_alt
Calculate the bonus as a percentage of the salary (e.g., 150% of salary).
arrow_right_alt
Create a column based on a different type of calculation, such as applying a tax rate.
arrow_right_alt
Work with a larger dataset and implement efficient methods for column operations.

help

常见问题

外企场景

探索更多题目 →

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继续模式

Create a New Column core interview pattern

用同一解题框架扩展到更多题目。

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同难度题单

简单

按当前难度继续强化稳定输出。

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