Use app online: www.shinyappstore.com/a/exploreModelMatrix
ExploreModelMatrix is a small R package that lets the user interactively explore a design matrix as generated by the model.matrix() R function. In particular, given a table with sample information and a design formula, ExploreModelMatrix illustrates the fitted values from a general linear model (or, more generally, the value of the linear predictor of a generalized linear model) for each combination of input variables, simplifying understanding and generation of contrasts. A number of other visualizations are also included in the interactive interface, particularly simplifying the interpretation of linear models.