[R] Interlacing two vectors

[kjetil brinchmann halvorsen]

On 21 Aug 2003 at 9:16, Murray Jorgensen wrote:

Hola!

I'm not sure if this is better, but if we can interlace first
1:n with (n+1):2n the rest is indexing:

> x <- 1:10
> y <- 1:10 + 0.5

> interl <- function(n) {
+    res <- numeric(2*n)
+    for (j in 1:n) {
+         res[2*j-1] <- j
+         res[2*j] <- n+j }
     res
+ }
> interl(4)
[1] 1 5 2 6 3 7 4 8
> c(x,y)[interl(10)]
 [1]  1.0  1.5  2.0  2.5  3.0  3.5  4.0  4.5  5.0  5.5  6.0  6.5  7.0 
 7.5  8.0
[16]  8.5  9.0  9.5 10.0 10.5 

You can do some testing to se what is fastest.

Kjetil Halvorsen


> I want to interlace two vectors. This I can do:
> 
>  > x <- 1:4
>  > z <- x+0.5
>  > as.vector(t(cbind(x,z)))
> [1] 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5
> 
> but this seems rather inelegant. Any suggestions?
> 
> Murray
> 
> -- 
> Dr Murray Jorgensen      http://www.stats.waikato.ac.nz/Staff/maj.html
> Department of Statistics, University of Waikato, Hamilton, New Zealand
> Email: maj at waikato.ac.nz                                Fax 7 838 4155
> Phone  +64 7 838 4773 wk    +64 7 849 6486 home    Mobile 021 1395 862
> 
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