Ordering of the 'individuals'
In most data sets, the individuals from whom data were recorded are unordered — any rearrangement of the rows of the data matrix would give the same information.
If the rows in the data matrix are recorded sequentially over time, the data are called a time series and the time-ordering can hold important information. A 'Time' variable can be added to the data matrix to capture the order.
Sugar content of grapes
Rainfall