[R] Vector recycling and zoo

[David Winsemius]

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