The R object is a log2 transformed expression matrix (HSMMdata) with 518 genes and 271 cells. This dataset is a subset of original gene expression profiles, which is available in the HSMMSingleCell package.
Trapnell, C., Cacchiarelli, D., Grimsby, J., Pokharel, P., Li, S., Morse, M., ... & Rinn, J. L. (2014). The dynamics and regulators of cell fate decisions are revealed by pseudotemporal ordering of single cells. Nature biotechnology.