EXAMPLE 9 Delta Encoding
Consider the following closing prices (rounded to the nearest integer) of the Standard & Poor’s (S&P) index of the stock prices of 500 companies in July 2013:
| 1615 | 1614 | 1615 | 1632 | 1640 | 1652 | 1653 | 1675 | 1680 | 1683 | 1676 |
| 1681 | 1689 | 1692 | 1696 | 1692 | 1686 | 1690 | 1692 | 1685 | 1686 | 1686 |
711
These numbers use 108 characters in all (counting spaces). To compress this dataset using the delta method, we start with the first number and continue by listing only the change from each entry to the next. So our list becomes
| 1615 | −1 | 1 | 17 | 8 | 12 | 1 | 22 | 5 | 3 | −7 | 5 | 8 | 3 | 4 | −4 | −6 | 4 | 2 | −7 | 1 | 0 |
This time we have used only 52 characters, counting the minus signs, to represent the same data, a savings of almost 52%.