[Rd] sum() returns NA on a long *logical* vector when nb of TRUE values exceeds 2^31

[Hervé Pagès]

Hi,

I have a long numeric vector 'xx' and I want to use sum() to count
the number of elements that satisfy some criteria like non-zero
values or values lower than a certain threshold etc...

The problem is: sum() returns an NA (with a warning) if the count
is greater than 2^31. For example:

   > xx <- runif(3e9)
   > sum(xx < 0.9)
   [1] NA
   Warning message:
   In sum(xx < 0.9) : integer overflow - use sum(as.numeric(.))

This already takes a long time and doing sum(as.numeric(.)) would
take even longer and require allocation of 24Gb of memory just to
store an intermediate numeric vector made of 0s and 1s. Plus, having
to do sum(as.numeric(.)) every time I need to count things is not
convenient and is easy to forget.

It seems that sum() on a logical vector could be modified to return
the count as a double when it cannot be represented as an integer.
Note that length() already does this so that wouldn't create a
precedent. Also and FWIW prod() avoids the problem by always returning
a double, whatever the type of the input is (except on a complex
vector).

I can provide a patch if this change sounds reasonable.

Cheers,
H.

-- 
Hervé Pagès

Program in Computational Biology
Division of Public Health Sciences
Fred Hutchinson Cancer Research Center
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Seattle, WA 98109-1024

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