Notes in RStudio package check results

[vincentvanhees]

While working on #53 I noticed that RStudio gives a NOTE that various objects are not declared:

I think the problem is that it is not clear in those places where those objects come from, for example they are not explicitly passed on by the function in which they are used. This makes the code less readable and that is why R warns us about it.

Further, I could not find where function time() is used, maybe it is a column time that you used without clarifying that it is a column instead of a function. This is why each object needs to be explicitly declared.