[Rd] NAs and rle

[Gabriel Becker]

Hi All,

A twitter user, Mike fc (@coolbutuseless) mentioned today that he was
surprised that repeated NAs weren't treated as a run by the rle function.

Now I know why they are not. NAs represent values which could be the same
or different from eachother if they were known, so from a purely conceptual
standpoint there is no way to tell whether they are the same and thus
constitute a run or not.

This conceptual strictness isnt universally observed, though, because we
get the following:

> unique(c(1, 2, 3, NA, NA, NA))

[1]  1  2  3 NA


Which means that rle(sort(x))$value is not guaranteed to be the same as
unique(x), which is a little strange (though likely of little practical
impact).


Personally, to me it also seems that, from a purely data-compression
standpoint, it would be valid to collapse those missing values into a run
of missing, as it reduces size in-memory/on disk without losing any
information.

Now none of this is to say that I suggest the default behavior be changed
(that would surely disrupt some non-trivial amount of existing code) but
what do people think of a  group.nas argument which defaults to FALSE
controlling the behavior?

As a final point, there is some precedent here (though obviously not at all
binding), as Bioconductor's Rle functionality does group NAs.

Best,
~G

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