Multiway data are observations arranged in an array indexed by several distinct kinds of variables, called modes (Kolda and Bader 2009). Higher-order
data have three or more modes and are represented by a tensor.
For example, measurements indexed by subject, measurement type, and time form a three-way
array .
The CANDECOMP/PARAFAC decomposition and Tucker decomposition analyze such data while retaining their multiple-index structure. Each factor describes variation along one mode.