[R] Why are integers coded as e.g. "2L" in R functions?

[Prof Brian Ripley]

On 15/05/2014 11:54, Alexander Engelhardt wrote:
> Hello R-help,
>
> I keep noticing R functions that don't compare integers like
>    if(x == 2)
> but instead
>    if(x == 2L)
>
> Is this a long integer? Also, when do the two notations have a different
> effect on the code?

2L is an integer. both in the mathematical sense and the sense of 
typeof().  2 is a double with a value that is a mathematical integer. 
They are stored differently, and in x == 2 'x' will be coerced to 
double, often unnecessarily.  Which is why careful authors write e.g.

length(x) == 2L

as length() the vast majority of the time gives an integer (especially 
where length-2 is expected).

> Thanks in advance,
>   Alex


-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
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