[R] Vector recycling and zoo
Gabor Grothendieck
ggrothendieck at gmail.com
Mon May 17 01:48:36 CEST 2010
Normally that would be written like this using the coredata extraction
function which extracts the data portion of a zoo object:
x$a / coredata( x$a[1] )
On Sun, May 16, 2010 at 7:32 PM, Sean Carmody <seancarmody at gmail.com> wrote:
> Thanks David,
>
> You comment made me realise that whereas when x is a data frame, x$a is a
> numeric vector,
> when x is of class zoo, x$a is also of class zoo, so the following does what
> I was expecting:
>
> x$a/as.numeric(x$a[1])
>
> Sean.
>
> On Sun, May 16, 2010 at 9:25 PM, David Winsemius <dwinsemius at comcast.net>wrote:
>
>>
>> On May 16, 2010, at 2:00 AM, Sean Carmody wrote:
>>
>> I am a bit confused about the different approaches taken to recycling in
>>> plain data frames and zoo objects. When carrying out simple arithmetic,
>>> dataframe seem to recycle single arguments, zoo objects do not. Here is an
>>> example
>>>
>>> x <- data.frame(a=1:5*2, b=1:5*3)
>>>> x
>>>>
>>> a b
>>> 1 2 3
>>> 2 4 6
>>> 3 6 9
>>> 4 8 12
>>> 5 10 15
>>>
>>>> x$a/x$a[1]
>>>>
>>> [1] 1 2 3 4 5
>>>
>>>> x <- zoo(x)
>>>> x$a/x$a[1]
>>>>
>>> 1
>>> 1
>>>
>>>>
>>>>
>>> I feel understanding this difference would lead me to a greater
>>> understanding of the zoo module!
>>>
>>
>> I think you do have misunderstandings about the zoo package but I do not
>> think it is in the area of vector recycling. Notice the effect of your
>> application of the zoo function to x:
>>
>> > x$a
>>
>> 1 2 3 4 5
>> 2 4 6 8 10
>> > x$a[1]
>> 1
>> 2
>>
>> You have in effect transposed the elements in x and are now getting a two
>> element column vector when requesting x$a[1]. The term vector recycling is
>> applied to situations where short vectors are reused starting with their
>> first elements until the necessary length is achieved. For instance if you
>> request:
>>
>> > data.frame(x=1:2, y=letters[1:10])
>> x y
>> 1 1 a
>> 2 2 b
>> 3 1 c
>> 4 2 d
>> 5 1 e
>> 6 2 f
>> 7 1 g
>> 8 2 h
>> 9 1 i
>> 10 2 j
>>
>> Or plot(1:10, col=c("red","green"))
>>
>>
>>> Sean.
>>>
>>> --
>>> Sean Carmody
>>>
>>
>>
>>
>
>
> --
> Sean Carmody
> Twitter: http://twitter.com/seancarmody
> Stable: http://mulestable.net/sean
>
> The Stubborn Mule
> Blog: http://www.stubbornmule.net
> Forum: http://mulestable.net/
>
> [[alternative HTML version deleted]]
>
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