Certain languages such as R and libraries/platforms such as Hadoop are used almost exclusively in data science. Should programming or configuration based questions for such languages, databases, libraries be on-topic?
I would say, questions pertaining to programming languages and tools as they are used in data science are relevant. Certainly I could ask a question about those tools that would be off topic, e.g. "Why is Hadoop's logo an elephant?"
A distinct but related question to "is it on topic" is "is this the best site for it"? The best site might depend on whether it's primarily a question about R as a programming language (stackoverflow), or primarily a question about statistical analysis using R as an example (crossvalidated), or primarily about R as a tool for data science (here).
Is the R language suitable for big data seems like a good question for DataScience.
Removal of statistically significant intercept term boosts R2 in linear model seems at home in Cross Validated, but might be on topic here as well.
How to sort a dataframe by column(s) in R seems a good fit for stackoverflow.
But many questions might be at home on multiple sites. I don't think the fact that a question could also be asked elsewhere necessarily means it's off-topic here.