In Python, a 2D list is a list of lists. Each element in the outer list represents a row, and each element in the inner list represents a column. The shape of a 2D list is the number of rows and columns it has. In this article, we will discuss how to find the shape of a 2D list in Python using the built-in function `len()`

and the NumPy library.

First, let's discuss how to find the shape of a 2D list using the built-in function `len()`

. To find the number of rows in a 2D list, we can use the `len()`

function on the outer list. To find the number of columns in a 2D list, we can use the `len()`

function on one of the inner lists. Here is an example of finding the shape of a 2D list using `len()`

:

```
# 2D list
my_2d_list = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
# number of rows
num_rows = len(my_2d_list)
print("Number of rows:", num_rows)
# number of columns
num_cols = len(my_2d_list[0])
print("Number of columns:", num_cols)
# shape
shape = (num_rows, num_cols)
print("Shape:", shape)
```

Output:

```
Number of rows: 3
Number of columns: 3
Shape: (3, 3)
```

Another way to find the shape of a 2D list is by using the NumPy library. The NumPy library provides a function called `shape`

which can be used to find the shape of a 2D list. Here is an example of finding the shape of a 2D list using NumPy:

```
# Importing NumPy library
import numpy as np
# 2D list
my_2d_list = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
# Converting list to NumPy array
my_2d_array = np.array(my_2d_list)
# Finding shape
shape = np.shape(my_2d_array)
print("Shape:", shape)
```

Output:

```
Shape: (3, 3)
```

It's important to note that the above examples assumes the 2D list is rectangular, with all the inner lists having the same length, If the 2D list is not rectangular, it means that each inner list has a different length, finding the shape becomes more complex and depends on the specific use case.

In conclusion, finding the shape of a 2D list in Python is a simple task that can be accomplished using the built-in function `len()`

or the NumPy library. The `len()`

function can be used to find the number of rows and columns in a 2D list, and the NumPy library provides the `shape`

function which can be used to find the shape of a 2D list. It's important to note that if the 2D list is not rectangular, finding the shape depends on the specific use case.

Another related topic that is closely related to finding the shape of a 2D list in Python is reshaping a 2D list. Reshaping a 2D list means changing the number of rows and columns in the list while maintaining the same number of elements. The NumPy library provides a function called `reshape()`

which can be used to reshape a 2D list. Here is an example of reshaping a 2D list using the `reshape()`

function:

```
import numpy as np
# 2D list
my_2d_list = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
# Converting list to NumPy array
my_2d_array = np.array(my_2d_list)
# Reshaping array
reshaped_array = my_2d_array.reshape(9, 1)
print(reshaped_array)
```

Output:

```
[[1]
[2]
[3]
[4]
[5]
[6]
[7]
[8]
[9]]
```

In this example, we have reshaped the 2D list from a 3×3 array to a 9×1 array while maintaining the same number of elements. The `reshape()`

function takes the number of rows and columns as arguments, in this case, we passed (9, 1) as arguments to reshape the array.

Another related topic is indexing and slicing a 2D list in Python. Indexing and slicing allow you to access specific elements or sublists within a 2D list. The basic syntax for indexing a 2D list is `my_2d_list[row][col]`

, where `row`

is the index of the row and `col`

is the index of the column. For example, to access the element at the second row and third column of a 2D list, you would use `my_2d_list[1][2]`

. Slicing a 2D list is also similar to indexing, but instead of accessing a single element, you are accessing a sublist. The basic syntax for slicing a 2D list is `my_2d_list[start_row:end_row][start_col:end_col]`

, where `start_row`

, `end_row`

, `start_col`

, and `end_col`

are the indices of the starting and ending rows and columns.

It's worth noting that NumPy array also provides a lot of functionality to perform mathematical and statistical operations on 2D array, such as finding the mean, standard deviation, sum and many more, it also supports broadcasting, which allows you to perform operations on entire arrays without the need of explicit loop.

In conclusion, finding the shape of a 2D list in Python is an important task that can be accomplished using the built-in function `len()`

or the NumPy library. Understanding how to reshape, index, and slice a 2D list is also important when working with 2D data. The NumPy library provides a lot of functionality to perform mathematical and statistical operations on 2D array, making it a powerful tool for data manipulation and analysis.

## Popular questions

- How can you find the shape of a 2D list in Python using the built-in function
`len()`

?

Answer: To find the number of rows in a 2D list, you can use the`len()`

function on the outer list. To find the number of columns in a 2D list, you can use the`len()`

function on one of the inner lists. The shape of the 2D list is represented as a tuple of the number of rows and columns. For example:

```
my_2d_list = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
num_rows = len(my_2d_list)
num_cols = len(my_2d_list[0])
shape = (num_rows, num_cols)
print("Shape:", shape)
```

Output: (3, 3)

- How can you find the shape of a 2D list in Python using the NumPy library?

Answer: The NumPy library provides a function called`shape()`

which can be used to find the shape of a 2D list. To use the`shape()`

function, you first need to convert the 2D list to a NumPy array using the`np.array()`

function. Then, you can use the`shape()`

function on the array to find the shape. For example:

```
import numpy as np
my_2d_list = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
my_2d_array = np.array(my_2d_list)
shape = np.shape(my_2d_array)
print("Shape:", shape)
```

Output: (3, 3)

- How can you reshape a 2D list in Python using the NumPy library?

Answer: The NumPy library provides a function called`reshape()`

which can be used to reshape a 2D list. To use the`reshape()`

function, you first need to convert the 2D list to a NumPy array using the`np.array()`

function. Then, you can use the`reshape()`

function on the array, passing in the desired number of rows and columns as arguments. For example:

```
import numpy as np
my_2d_list = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
my_2d_array = np.array(my_2d_list)
reshaped_array = my_2d_array.reshape(9, 1)
print(reshaped_array)
```

Output: [[1], [2], [3], [4], [5], [6], [7], [8], [9]]

- How can you index and slice a 2D list in Python?

Answer: To index a specific element in a 2D list, you can use the syntax`my_2d_list[row][col]`

, where`row`

is the index of the row and`col`

is the index of the column. For example, to access the element at the second row and third column of a 2D list, you would use`my_2d_list[1][2]`

. To slice a sublist from a 2D list, you can use the syntax `my_2d_list[start_row

### Tag

Shape