> Richard O'Keefe
> on Wed, 21 Dec 2022 16:44:51 +1300 writes:
> Lack of consensus: I should mention Python's // operator,
> which does flooring division. I should mention Common
> Lisp, where (floor - -), (ceiling - -), (round - -), and
> (truncate - -) all return a
Lack of consensus:
I should mention Python's // operator, which does
flooring division.
I should mention Common Lisp, where (floor - -),
(ceiling - -), (round - -), and (truncate - -)
all return a quotient and appropriate remainder.
I should mention Smalltalk, where // and \\ are
ent: Tuesday, December 20, 2022 1:53 AM
To: Richard O'Keefe
Cc: r-help@r-project.org
Subject: Re: [R] Integer division
Thanks Richard,
the "rounding claim" was my mistake (as I replied to Martin), I should said
"truncates toward zero" as you explain.
However, my p
Thanks Richard,
the "rounding claim" was my mistake (as I replied to Martin), I should
said "truncates toward zero" as you explain.
However, my point was that these two mathematical functions should be
defined in the documentation, as you also say. And I was surprised that
there is no
The Fortran '08 standard says <<
One operand of type integer may be divided by another operand of type
integer. Although the mathematical
quotient of two integers is not necessarily an integer, Table 7.2 specifies
that an expression involving the division
operator with two operands of type integer
"It would probably be helpful to add a short paragraph to ?Arithmetic
about the fact that R's %% uses the "floored" version, as
recommended by Donald Knuth and as documented on the above
Wikipedia page."
Agreed (who am I to disagree?!).
But perhaps something simpler like:
"a %% b must always
> Jeff Newmiller
> on Mon, 19 Dec 2022 08:37:32 -0800 writes:
> See https://en.m.wikipedia.org/wiki/Modulo_operation,
> Variants of the definition, esp the point that Knuth
> recommended the floor definition. The behavior of %/%
> follows from the definition of %%
See https://en.m.wikipedia.org/wiki/Modulo_operation, Variants of the
definition, esp the point that Knuth recommended the floor definition. The
behavior of %/% follows from the definition of %% given the documented relation
in ?Arithmetic.
R is not obligated to repeat the mistakes of C or
If R does exactly what it says it does, why are you surprised, whether or
not that is what other languages do? (Please excuse my fractured English).
(Note: -8 = 1 + 3*(-3) = (-8 %% 3) + 3 * (-8 %/% 3 ), exactly as the
Help excerpt you cited says)
Of course, one may always question the wisdom
Den 2022-12-19 kl. 15:41, skrev Martin Maechler:
Göran Broström
on Mon, 19 Dec 2022 14:22:00 +0100 writes:
> I have a long vector x with five-digit codes where the
> first digit of each is of special interest, so I extracted
> them through
>> y <- x %/% 1
> Göran Broström
> on Mon, 19 Dec 2022 14:22:00 +0100 writes:
> I have a long vector x with five-digit codes where the
> first digit of each is of special interest, so I extracted
> them through
>> y <- x %/% 1
> but to my surprise y contained the value -1
I have a long vector x with five-digit codes where the first digit of
each is of special interest, so I extracted them through
> y <- x %/% 1
but to my surprise y contained the value -1 in some places. It turned
out that x contains -1 as a symbol for 'missing value' so in effect I
found
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