R help - May 2009 - Behavior of seq with vector from

Hello,

I want to use seq with multiple from values and am getting unexpected
(to me) behavior. I'm wondering if this behavior is intentional or not.
> seq(2, by=3, length.out=4)
[1]  2  5  8 11
> seq(3, by=3, length.out=4)
[1]  3  6  9 12

Now if I want the combined sequence, I thought I could pass in c(2,3),
and I get:
> seq(c(2,3), by=3, length.out=8)
[1]  2  6  8 12 14 18 20 24

However, the result is not what I expected (i.e. what I wanted):
[1]  2  3  5  6  8  9 11 12

It seems that this is a consequence of vector recycling during the
summation in seq.default:
  if (missing(to)) from + (0L:(length.out - 1L)) * by

To get the value I want, I am using the following code:
> sort(as.vector(apply(array(c(2,3)), 1, seq, by=3,length.out=4)))
[1]  2  3  5  6  8  9 11 12

So two questions:
1. Is seq designed/intended to be used with a vector from argument, and
is this the desired behavior?
2. If so, is there a cleaner way of implementing what I want?

Thanks,
Brian




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Rowe, Brian Lee Yung (Portfolio Analytics) wrote:
> 
> Hello,
> 
> I want to use seq with multiple from values and am getting unexpected
> (to me) behavior. I'm wondering if this behavior is intentional or not.
> 
>> seq(2, by=3, length.out=4)
> [1]  2  5  8 11
> 
>> seq(3, by=3, length.out=4)
> [1]  3  6  9 12
> 
> Now if I want the combined sequence, I thought I could pass in c(2,3),
> and I get:
>> seq(c(2,3), by=3, length.out=8)
> [1]  2  6  8 12 14 18 20 24
> 
> However, the result is not what I expected (i.e. what I wanted):
> [1]  2  3  5  6  8  9 11 12
> 
> It seems that this is a consequence of vector recycling during the
> summation in seq.default:
>   if (missing(to)) from + (0L:(length.out - 1L)) * by
> 
> To get the value I want, I am using the following code:
>> sort(as.vector(apply(array(c(2,3)), 1, seq, by=3,length.out=4)))
> [1]  2  3  5  6  8  9 11 12
> 
> So two questions:
> 1. Is seq designed/intended to be used with a vector from argument, and
> is this the desired behavior?
> 2. If so, is there a cleaner way of implementing what I want?
> 
> Thanks,
> Brian
> 
> 
Don't know if this is "cleaner" or not.
It may be a little bit too tricky.

c(outer(2:3,seq(0,by=3,length.out=4),"+"))

  Can compress your example slightly:

c(t(apply(matrix(2:3), 1, seq, by=3,length.out=4)))

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Hi,

Perhaps you can try this,

> seq.weave <- function(froms, by, length,  ... ){
> 	c(
> 		matrix(c(sapply(froms, seq, by=by, length = length/2,  ...)),
> 		nrow=length(froms), byrow=T)
> 		)
> }
>
> seq.weave(c(2, 3), by=3, length=8)
> seq.weave(c(2, 3, 4), by=2, length=8)

HTH,

baptiste

On 21 May 2009, at 21:08, Rowe, Brian Lee Yung (Portfolio Analytics)  
wrote:
> Hello,
>
> I want to use seq with multiple from values and am getting unexpected
> (to me) behavior. I'm wondering if this behavior is intentional or  
> not.
>
>> seq(2, by=3, length.out=4)
> [1]  2  5  8 11
>
>> seq(3, by=3, length.out=4)
> [1]  3  6  9 12
>
> Now if I want the combined sequence, I thought I could pass in c(2,3),
> and I get:
>> seq(c(2,3), by=3, length.out=8)
> [1]  2  6  8 12 14 18 20 24
>
> However, the result is not what I expected (i.e. what I wanted):
> [1]  2  3  5  6  8  9 11 12
>
> It seems that this is a consequence of vector recycling during the
> summation in seq.default:
>  if (missing(to)) from + (0L:(length.out - 1L)) * by
>
> To get the value I want, I am using the following code:
>> sort(as.vector(apply(array(c(2,3)), 1, seq, by=3,length.out=4)))
> [1]  2  3  5  6  8  9 11 12
>
> So two questions:
> 1. Is seq designed/intended to be used with a vector from argument,  
> and
> is this the desired behavior?
> 2. If so, is there a cleaner way of implementing what I want?
>
> Thanks,
> Brian
>
>
>
>
> --------------------------------------------------------------------------
> This message w/attachments (message) may be privileged...{{dropped:26}}

Rowe, Brian Lee Yung (Portfolio Analytics) wrote:
....
> To get the value I want, I am using the following code:
>> sort(as.vector(apply(array(c(2,3)), 1, seq, by=3,length.out=4)))
> [1]  2  3  5  6  8  9 11 12
> 
> So two questions:
> 1. Is seq designed/intended to be used with a vector from argument, and
> is this the desired behavior?
> 2. If so, is there a cleaner way of implementing what I want?
1. Hmm, not really. NA.

2. I'd view it as an outer sum, stringed out to a single vector, hence:
> c(outer(c(2,3), seq(0,,3,4), "+"))
[1]  2  3  5  6  8  9 11 12


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