The sample market basket

Each transaction numbered 1-10 listed previously represents a basket of items purchased by a shopper. These are typically all items that are associated with a particular transaction or invoice. Each basket is enclosed within braces {}, and is referred to as an itemset. An itemset is a group of items that occur together.

Market basket algorithms construct rules in the form of:

Itemset{x1,x2,x3 ...} --> Itemset{y1,y2,y3...}. 

This notation states that buyers who have purchased items on the left-hand side of the formula (lhs) have a propensity to purchase items on the right-hand side (rhs). The association is stated using the à symbol, which can be interpreted as implies.

Note

The lhs of the notation is also known as the antecedent, and the rhs is known as the consequence. If nothing appears on either the left-hand side or right-hand side there is no specific association rule for those items; however, it also means that those items have appeared in the basket.