Since the virtue and reliability of Wikis was brought up, I created a R
Wiki page for this at
http://www.sciviews.org/_rgui/wiki/doku.php?id=beginners:surprises:emptysetfuncs
:-)
Anyone: please correct errors and improve it!
Tony Plate
Duncan Murdoch wrote:
> On 1/9/2006 1:27 PM, Liaw, Andy wr
On Jan 9, 2006, at 3:35 PM, Kjetil Halvorsen wrote:
> But this thread seems to have pointed to some inconsistencies:
>
>> cumprod( numeric(0) )
> numeric(0)
>> cumsum( numeric(0) )
> numeric(0)
>
> shouldn't this give the same as prod() and sum() in this case?
No - as Thomas explained very nicely
But this thread seems to have pointed to some inconsistencies:
> cumprod( numeric(0) )
numeric(0)
> cumsum( numeric(0) )
numeric(0)
shouldn't this give the same as prod() and sum()
in this case?
Same with cummin() and cummax().
Kjetil
On 1/9/06, Duncan Murdoch <[EMAIL PROTECTED]> wrote:
>
> On
On Mon, 9 Jan 2006, Thomas Lumley wrote:
> On Mon, 9 Jan 2006, Martin Morgan wrote:
>
>> I guess I have to say yes, I'd exepct
>>
>> x <- 1:10
>> sum(x[x>10]) ==> numeric(0)
>>
>> this would be reinforced by recongnizing that numeric(0) is not zero,
>> but nothing. I guess the summation over an
On Mon, 9 Jan 2006, Martin Morgan wrote:
> I guess I have to say yes, I'd exepct
>
> x <- 1:10
> sum(x[x>10]) ==> numeric(0)
>
> this would be reinforced by recongnizing that numeric(0) is not zero,
> but nothing. I guess the summation over an empty set is an empty set,
> rather than a set contain
Duncan Murdoch <[EMAIL PROTECTED]> writes:
> On 1/9/2006 1:27 PM, Liaw, Andy wrote:
>> If you haven't seen this in your math courses, perhaps this would help:
>> http://en.wikipedia.org/wiki/Empty_set
>>
>
> This is what is so great about Wikipedia: it gives certainty where
> I'd only call it a f
On 1/9/2006 1:27 PM, Liaw, Andy wrote:
> If you haven't seen this in your math courses, perhaps this would help:
>
> http://en.wikipedia.org/wiki/Empty_set
>
This is what is so great about Wikipedia: it gives certainty where I'd
only call it a fairly standard convention. ;-)
Duncan Murdoch
If you haven't seen this in your math courses, perhaps this would help:
http://en.wikipedia.org/wiki/Empty_set
which says, in part:
Operations on the empty set
Operations performed on the empty set (as a set of things to be operated
upon) can also be confusing. (Such operations are nullary oper
I guess I have to say yes, I'd exepct
x <- 1:10
sum(x[x>10]) ==> numeric(0)
this would be reinforced by recongnizing that numeric(0) is not zero,
but nothing. I guess the summation over an empty set is an empty set,
rather than a set containing the number 0. Certainly these
exp(x[x>10]) ==> nume
The way to think about it is:
prod(rep(x,n)) == x^n
and that works for n=0 too.
On 1/9/06, Martin Morgan <[EMAIL PROTECTED]> wrote:
> I'm a little confused. I understand that numeric(0) means an empty
> numeric vector, not the number 0 expressed as numeric. As it is now,
> prod(numeric(0)) ge
On 1/9/2006 12:40 PM, Martin Morgan wrote:
> I'm a little confused. I understand that numeric(0) means an empty
> numeric vector, not the number 0 expressed as numeric. As it is now,
> prod(numeric(0)) generates something -- a vector of length 1
> containing the number 1 -- from nothing. I would ha
I'm a little confused. I understand that numeric(0) means an empty
numeric vector, not the number 0 expressed as numeric. As it is now,
prod(numeric(0)) generates something -- a vector of length 1
containing the number 1 -- from nothing. I would have expected
prod(numeric(0)) ==> numeric(0)
this
> "Ben" == Ben Bolker <[EMAIL PROTECTED]>
> on Sun, 08 Jan 2006 21:40:05 -0500 writes:
Ben> Duncan Murdoch wrote:
>> On 1/8/2006 9:24 PM, Ben Bolker wrote:
>>
>>> It surprised me that prod(numeric(0)) is 1. I guess if
>>> you say (operation(nothing) == identity el
Duncan Murdoch wrote:
> On 1/8/2006 9:24 PM, Ben Bolker wrote:
>
>>It surprised me that prod(numeric(0)) is 1.
>> I guess if you say (operation(nothing) == identity
>> element) this makes sense, but ??
>
>
> What value were you expecting, or were you expecting an error? I can't
> think how
On 1/8/2006 9:24 PM, Ben Bolker wrote:
>It surprised me that prod(numeric(0)) is 1.
> I guess if you say (operation(nothing) == identity
> element) this makes sense, but ??
What value were you expecting, or were you expecting an error? I can't
think how any other value could be justified, an
It surprised me that prod(numeric(0)) is 1.
I guess if you say (operation(nothing) == identity
element) this makes sense, but ??
Looking in the code, this makes sense:
basically (s=1; for i=0 to length(x),
multiply s by x[i]) -- which comes out to 1.
What *should* prod(numeric(0)) prod
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