# 5.16 Two-Dimensional Lists¶

- Lists can contain other lists as elements.
- Typical use is to represent tables of values consisting of information arranged in rows and columns.
- To identify a particular table element, we specify two indices—the first identifies the element’s row, the second the element’s column.

### Creating a Two-Dimensional List¶

In [1]:

    a = [[77, 68, 86, 73], [96, 87, 89, 81], [70, 90, 86, 81]]

Writing the list as follows makes its row and column tabular structure clearer:

    a = [[77, 68, 86, 73],  # first student's grades
         [96, 87, 89, 81],  # second student's grades
         [70, 90, 86, 81]]  # third student's grades

### Illustrating a Two-Dimensional List¶

### Identifying the Elements in a Two-Dimensional List¶

- Output the rows of the preceding two-dimensional list.

In [2]:

    for row in a:
        for item in row:
            print(item, end=' ')
        print()

    77 68 86 73
    96 87 89 81
    70 90 86 81

### How the Nested Loops Execute¶

In [3]:

    for i, row in enumerate(a):
        for j, item in enumerate(row):
            print(f'a[{i}][{j}]={item} ', end=' ')
        print()

    a[0][0]=77  a[0][1]=68  a[0][2]=86  a[0][3]=73
    a[1][0]=96  a[1][1]=87  a[1][2]=89  a[1][3]=81
    a[2][0]=70  a[2][1]=90  a[2][2]=86  a[2][3]=81

- Outer `for` statement iterates over the list’s ows one row at a time.
- During each iteration of the outer `for` statement, the inner `for` statement iterates over each column in the current row.

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