Lee, B.H., Ryu, S.W. and Choi, Y.S.(2021). vlda: An R Package for Statistical Visualization of Multidimensional Longitudinal Data, Communications for Statistical Applications and Methods, 28(4), 369-391. SCOPUS

The vlda is an R (R Development Core Team et al., 2011) package which provides functions for visualization
of multidimensional longitudinal data. In particular, the R package vlda was developed to assist in producing
a plot that more effectively expresses changes over time for two different types (long format and wide format),
uses a consistent calling scheme for longitudinal data. The main features of this package is that it allows us
to identify the relationship between categories and x-x-x-x-objects using the indicator matrix with x-x-x-x-object information,
as well as to cluster x-x-x-x-objects. This can be used to understand trends in observations over time in addition to
identifying relative relationships at a simple visualization level. It also offers a new interactive implementation to
perform additional interpretation, therefore it is useful for longitudinal data visual analysis. Due to the synergistic
relationship between the existing VLDA plot and interactive features, the user is empowered by a refined observe
the visual aspects of the VLDA plot layout. Furthermore, it allows the projection of supplementary information
(supplementary x-x-x-x-objects and variables) that often occur in longitudinal data of graphs. In this study, practical
examples are provided to highlight the implemented methods of real applications.

Keywords: vlda, visualization, longitudinal data, R.