Colors and plot symbols can be chosen according to the levels of factors. Points can be connected by lines as desired, and overlayed plots can be produced. In most applications, data are given as a rectangular data set, i.e. a number of variates and factors of the same length, which is the number of 'records' or 'experimental units' or 'patients' or 'persons' or 'runs' or 'plots' or whatever, depending on the applied context. We shall use the word units. All ISU commands for which this is relevant obey restrictions, in the sense that only units present are taken into account.
Restrictions act in parallel on all vectors, independently of their lengths.
Parallel restrictions on vectors of different lengths are usually meaningless. If it is declared before, it must be a variate of length 100. Factors can also be handled in this way, and many transformations that are not just 'unit by unit' are also possible. All model fit commands involve the concept of a model formula, i.e. a code for a linear expression involving linear effects of covariates, effects of factors, interactions between factors etc. The design matrix determined by a model formula is not physically stored.