R: Why my vector is disordered?

Question

Let say I have this zoo vector

mine <- zoo(c(rep(0,4),rep(1,4),rep(0,5),rep(1,23),rep(0,4),rep(1,2)),as.chron(seq(1:42)))

And I want to extract several elements in some order

> mine[14]
01/15/70 
       1 
> mine[5]
01/06/70 
       1 
> mine[41]
02/11/70 
       1 

It works!. But now I try to do it in a different way

zz <- c(14, 5, 41)
mine[zz]

01/06/70 01/15/70 02/11/70 
       1        1        1 

I don't know why I get it in a different order. How can I keep the order I want, the order of my list ?? I don't mind if it's a list, a vector, by columns or by row, but I'd like to get it in the order I've asked for.

cheers

Answer 1

The answer to why zoo does this is that it has a method for the function [ ([.zoo), and it creates a new zoo object from the subsetted values, which it logically wants to reorder so that it is a valid zoo object.

You can achieve what you want by accessing the time indices and data via the relevant accessor functions:

> index(mine)[c(14, 5, 41)]
[1] 01/15/70 01/06/70 02/11/70
> coredata(mine)[c(14, 5, 41)]
[1] 1 1 1

If you want to combine this into a single step, write your own fun to do:

myExtract <- function(x, want) {
    out <- coredata(mine)[want]
    names(out) <- index(x)[want]
    out
}

Which gives:

> myExtract(mine, want = c(14, 5, 41))
01/15/70 01/06/70 02/11/70 
       1        1        1