List Property

A list property is a property whose value is a list of several values rather than a single one — such as the items in a cart on one event.

A list property is needed when an event inherently has several values at once; a cart-viewed event might have five items, and breaking it into five separate events both inflates the data and severs their relationship. Its value is being able to ask 'users who had item A' or 'any tag that co-occurred with this tag.' But a list property has two difficulties: breaking down by it is more complex than a single-valued property because one event falls into several groups and the percentages can sum past 100, and high cardinality — if the lists are long and varied — makes storage and reporting heavy. So keep a list for genuinely multiple values, not for something a single property would solve.