[Feature Request] Initialize selected subjects in the dataset

[birajstha]

When the dataset is huge, it takes a while to parse through the whole dataset. It would be nice if we could selectively parse the dataset for few or just one subject.
This would be a Luxury Feature (in Steve's words)

[clane9]

Thanks for the suggestion @birajstha. This feature has been added in #48. Please give it a try and see if it meets your needs 🙏.