I've used this sentence but it just sounds wrong a posteriori:
"The missing data is the weekends' one."
I'm trying to say data is missing only on the weekends.
I know there are more elegant ways of saying that; but is it at least correct?
Some people think that "data" is plural and so "one" would not work in this sentence. (Try replacing "data" with "numbers" in your sentence and see if it works.)
Other people think "data" is uncountable and so, again, "one" would not work in this sentence. (Try replacing "data" with "information" in your sentence and see if it works.)
See for, example, the discussion on the Oxford Dictionaries blog:
In particular, the usage of data still generates debate: I reckon they’re deserving of a blog all to themselves, so here goes. What do these two nouns have in common? Firstly, they’re Latin plurals which are now firmly established in English; secondly, many people are in a quandary about whether they should be treated as singular
Overall, the data gives some mixed messages.
The data were gathered from the World Resources Institute.
Maybe just removing "one" solves the problem? (But I would probably rewrite the sentence).
I think it is correct, assuming that "one" refers, in some way to something tied back to the missing data. For instance, imagine that sentence as part of a dialog:
Bob: What's the biggest problem you have during the week, and the biggest problem you have on your weekends?
Jack: The missing data is the weekends' one.
So, in short, to answer your question, sure, the sentence is grammatically correct. (Without further context, though, it's also completely cryptic.)
As artfully pointed out in another answer, your sentence is grammatical in context.
However, it would likely be construed as ungrammatical outside of that particular context.
Here are some other possible ways of expressing it that wouldn't depend on context:
All weekend data is missing.
The missing data relates only to weekends.
The data is only missing information from weekends.
Gaps in the data only occur on weekends.