Data tables are row-by-column matrices, and obviously they can range in size from one row by one column to many rows by many columns. You might have come across the colloquial expressions tall table and wide table, or even tall, narrow table and short, wide table, or some variation thereof.
These expressions are a handy way of describing the fundamental way in which the data is structured or categorized in a table. In a tall table, a list of categories is contained under a single column and a second column lists values associated with each of those categories. In a wide table, each category gets its own column and the associated values appear under it.
Consider the airline delay data we used previously in this chapter. As it stands, the data is wide. There is a column for every type of delay, for example:
As a tall table, it looks very different...
