R help - Jan 2008 - question about order

I have a data vector as following:
> z
 [1] 183.1370 201.9610 113.7250 140.7840 156.2750  42.1569  42.1569  42.1569
 [9] 240.1960 308.4310  42.1569  42.1569  42.1569  42.1569  42.1569  42.1569
[17]  42.1569  42.1569  42.1569  42.1569 279.8040  42.1569  42.1569

when I sort, it gave me the right order
> sort(z)
 [1]  42.1569  42.1569  42.1569  42.1569  42.1569  42.1569  42.1569  42.1569
 [9]  42.1569  42.1569  42.1569  42.1569  42.1569  42.1569  42.1569 113.7250
[17] 140.7840 156.2750 183.1370 201.9610 240.1960 279.8040 308.4310

BUT when I use the order, the returned index is strange and not right.
 You can check the first 4 values.
> order (z)
 [1]  6  7  8 11 12 13 14 15 16 17 18 19 20 22 23  3  4  5  1  2  9 21 10

I am not sure why R does not order it correctly when handling a vector
with repetitive values.

I use just the first 4 values of z, then it ordered
correctly.
> order (z[1:4])
[1] 3 4 1 2

Can someone help?  What is the problem here? Is this a R bug?  How to
order when handling a vector with repetitive values?

-- 
Waverley @ Palo Alto

that seems right....

order() gives you the indexes "idx" such that x[idx] == sort(x)

 > set.seed(123)
 > x <- rnorm(10)
 > idx <- order(x)
 > identical(x[idx], sort(x))
[1] TRUE

best
b

On Jan 28, 2008, at 8:19 PM, Waverley wrote:
> I have a data vector as following:
>> z
> [1] 183.1370 201.9610 113.7250 140.7840 156.2750  42.1569  42.1569   
> 42.1569
> [9] 240.1960 308.4310  42.1569  42.1569  42.1569  42.1569  42.1569   
> 42.1569
> [17]  42.1569  42.1569  42.1569  42.1569 279.8040  42.1569  42.1569
>
> when I sort, it gave me the right order
>
>> sort(z)
> [1]  42.1569  42.1569  42.1569  42.1569  42.1569  42.1569  42.1569   
> 42.1569
> [9]  42.1569  42.1569  42.1569  42.1569  42.1569  42.1569  42.1569  
> 113.7250
> [17] 140.7840 156.2750 183.1370 201.9610 240.1960 279.8040 308.4310
>
> BUT when I use the order, the returned index is strange and not right.
> You can check the first 4 values.
>> order (z)
> [1]  6  7  8 11 12 13 14 15 16 17 18 19 20 22 23  3  4  5  1  2  9  
> 21 10
>
> I am not sure why R does not order it correctly when handling a vector
> with repetitive values.
>
> I use just the first 4 values of z, then it ordered correctly.
>> order (z[1:4])
> [1] 3 4 1 2
>
> Can someone help?  What is the problem here? Is this a R bug?  How to
> order when handling a vector with repetitive values?
>
> -- 
> Waverley @ Palo Alto
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.

On Mon, 28 Jan 2008, Waverley wrote:
> I have a data vector as following:
> > z
>  [1] 183.1370 201.9610 113.7250 140.7840 156.2750  42.1569  42.1569 
42.1569
>  [9] 240.1960 308.4310  42.1569  42.1569  42.1569  42.1569  42.1569 
42.1569
> [17]  42.1569  42.1569  42.1569  42.1569 279.8040  42.1569  42.1569
>
> when I sort, it gave me the right order
>
> > sort(z)
>  [1]  42.1569  42.1569  42.1569  42.1569  42.1569  42.1569  42.1569 
42.1569
>  [9]  42.1569  42.1569  42.1569  42.1569  42.1569  42.1569  42.1569
113.7250
> [17] 140.7840 156.2750 183.1370 201.9610 240.1960 279.8040 308.4310
>
> BUT when I use the order, the returned index is strange and not right.
>  You can check the first 4 values.
> > order (z)
>  [1]  6  7  8 11 12 13 14 15 16 17 18 19 20 22 23  3  4  5  1  2  9 21 10
Seems ok to me. Maybe you are looking for rank()?

Order gives the ordering permutation, rank the inverse, i.e.:

R> z2 <- sort(z)
R> identical(z2, z[order(z)])
[1] TRUE
R> identical(z, z2[rank(z)])
[1] TRUE

hth,
Z
> I am not sure why R does not order it correctly when handling a vector
> with repetitive values.
>
> I use just the first 4 values of z, then it ordered correctly.
> > order (z[1:4])
> [1] 3 4 1 2
>
> Can someone help?  What is the problem here? Is this a R bug?  How to
> order when handling a vector with repetitive values?
>
> --
> Waverley @ Palo Alto
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>
>