Major cell

In the APL array model and leading axis theory, a major cell, or item, is a cell of an array which has rank one smaller than the rank of the array, or equal to it if the array is a scalar. The number of major cells in an array is its Tally, and a function can be called on the major cells of an array individually by applying it with rank  using the Rank operator. Functions designed to follow leading axis theory often manipulate the major cells of an array. For example, Reverse First is considered the primary form of Reverse in leading-axis languages because it can be interpreted as reversing the major cells of its argument; J removes last-axis Reverse entirely.

Examples
is an array with shape. Using Tally we see that the number of major cells in  is the first element of the shape,  : We can separate 's major cells using Enclose with rank  : Given another array  we can search for cells of   which match major cells of. High-rank Index-of always searches for right argument cells whose rank matches the rank of a left argument major cell: if the right argument is a vector and not a matrix then it searches for the entire vector rather than its major cells (which are scalars).