Difference between "Data" and "Values" in R

You are not missing a "major concept in R". What you are missing is that RStudio has chosen for reasons of its own (thinking it was helping users no doubt) to segregate dataframes from other objects such as lists without the "data.frame" class. There is no "Data" or "Values" class in R and you won't find that distinction in the R Manuals. That's RStudio at work and not part of R. As I read the Jonathon-answer to the cited question, my guess is that the decision is based on whether the R object has a dimension attribute since he says matrices and frame would also be listed in "Values". I think a more accurate labeling would be "Dimensioned Objects" and "Non-dimensioned, non-language Objects". I was a bit surprised that lists get displayed but atomic vectors do not (contrary to Jonathon). Maybe there's a switch that can be thrown somewhere to display names of atomic vectors in that panel?

This goes in the Data section:

dat <- data.frame(a=1:10, b=letters[1:10])

And this would move it to the Values section:

dat <- unclass(dat)

I will admit that there have been times when I wanted this information and (eventually) got it by running something like this:

> ls()[ lapply( mget( ls() ) , class) == "data.frame" ]
[1] "air1"   "air2"   "dat"    "df"     "dfCord" "fsub"   "mtcars" "test"  

This is purely a difference in RStudio. 'Data' objects are S4 objects, environments, and objects with dimensions. There may be more, these are the few I have found so far. 'Value' objects are objects that are neither functions nor 'Data' objects.

Edit : Upon further inspection, it appears as though 'Values' in RStudio are atomic objects with less than 2 dimensions. I hope this helps.