#2885 Rename Columns - Solution

DataFrame students
+-------------+--------+
| Column Name | Type   |
+-------------+--------+
| id          | int    |
| first       | object |
| last        | object |
| age         | int    |
+-------------+--------+

Write a solution to rename the columns as follows:

id to student_id
first to first_name
last to last_name
age to age_in_years

The result format is in the following example.

Example 1:
Input:
+----+---------+----------+-----+
| id | first   | last     | age |
+----+---------+----------+-----+
| 1  | Mason   | King     | 6   |
| 2  | Ava     | Wright   | 7   |
| 3  | Taylor  | Hall     | 16  |
| 4  | Georgia | Thompson | 18  |
| 5  | Thomas  | Moore    | 10  |
+----+---------+----------+-----+
Output:
+------------+------------+-----------+--------------+
| student_id | first_name | last_name | age_in_years |
+------------+------------+-----------+--------------+
| 1          | Mason      | King      | 6            |
| 2          | Ava        | Wright    | 7            |
| 3          | Taylor     | Hall      | 16           |
| 4          | Georgia    | Thompson  | 18           |
| 5          | Thomas     | Moore     | 10           |
+------------+------------+-----------+--------------+
Explanation: 
The column names are changed accordingly.

In #2885 Rename Columns, the goal is to modify the names of columns in the query result without changing the underlying table structure. This is commonly done in SQL when the output format requires specific column names for readability or compatibility.

The standard approach is to use the aliasing feature in SQL with the AS keyword. While selecting columns from a table, you can assign a new name to each column using SELECT column_name AS new_name. This only changes the column name in the result set and does not affect the actual schema of the database.

This method is efficient because the database engine simply maps the alias during query execution. The query still performs a normal table scan or retrieval depending on the underlying dataset size. Since no additional data structures or transformations are required, the approach is straightforward and highly optimized.

Overall, the solution relies on proper SQL syntax and understanding how result-set aliases work.

Approach	Time Complexity	Space Complexity
Using SQL column aliases with `AS`	O(n)	O(1)

Solutions (4)

Data Structure Manipulation

This approach focuses on manipulating the data structures that hold the DataFrame or its equivalent to rename the columns. The idea is to access the data structure directly and modify the column headers.

Time Complexity: O(1) as renaming columns in a DataFrame does not depend on the number of rows.
Space Complexity: O(1), no additional space required beyond the rename operation.

Python JavaScript

1function renameColumns(objArray) {
2    return objArray.map(({ id, first, last, age, ...rest }) => ({
3        student_id: id,
4        first_name: first,
5        last_name: last,
6        age_in_years: age,
7        ...rest
8    }));
9}
10
11// Example Usage
12const students = [
13    { id: 1, first: 'Mason', last: 'King', age: 6 },
14    { id: 2, first: 'Ava', last: 'Wright', age: 7 },
15    { id: 3, first: 'Taylor', last: 'Hall', age: 16 },
16    { id: 4, first: 'Georgia', last: 'Thompson', age: 18 },
17    { id: 5, first: 'Thomas', last: 'Moore', age: 10 }
18];
19
20console.log(renameColumns(students));

Explanation

In JavaScript, an array of objects can represent the data. Using array map combined with object destructuring, we can easily transform and rename the column keys in each object.

Library Specific Utility

This approach relies on using specific libraries available for each programming language that are geared towards data manipulation. These libraries often offer built-in functionalities for renaming columns effortlessly.

Time Complexity: O(1) since column renaming is independent of the data in the table.
Space Complexity: O(1) because it modifies column names in-place.

C#Java

1using System;
2using System.Collections.Generic;
3using System.Data;
4
5class Program {
6    static void Main() {
        DataTable students = new DataTable();
        students.Columns.Add("id", typeof(int));
        students.Columns.Add("first", typeof(string));
        students.Columns.Add("last", typeof(string));
        students.Columns.Add("age", typeof(int));

        students.Rows.Add(1, "Mason", "King", 6);
        students.Rows.Add(2, "Ava", "Wright", 7);
        students.Rows.Add(3, "Taylor", "Hall", 16);
        students.Rows.Add(4, "Georgia", "Thompson", 18);
        students.Rows.Add(5, "Thomas", "Moore", 10);

        RenameColumns(students);

        foreach (DataRow row in students.Rows) {
            Console.WriteLine(string.Join(", ", row.ItemArray));
        }
    }

    static void RenameColumns(DataTable table) {
        table.Columns["id"].ColumnName = "student_id";
        table.Columns["first"].ColumnName = "first_name";
        table.Columns["last"].ColumnName = "last_name";
        table.Columns["age"].ColumnName = "age_in_years";
    }
}