[R-sig-finance] Sorting

[Rainer Böhme]

Hi Lorenzo,

# given this 2 x N matrix

N <- 10^5
A <- matrix(rnorm(2*N),2)

# use the following statement to sort the column vectors by their elements
in the i-th row

i <- 1
A <- A[,order(A[i,])]

Hope this helps,
Rainer

> Good Morning Lorenzo,
>
> I had a look at ?sort and it said "For ordering along more than one
> variable, e.g., for sorting data frames, see 'order'." So I had a look
> at ?order... and popped down to the examples and it talks about
> ordering a dataframe - not the clearest of examples, but hey :-)
> Sometimes the obvious is the hardest to see :-)
>
> cheers!
> Sean
>
>
> On 16/11/05, L.Isella <L.Isella at myrealbox.com> wrote:
>> Dear All,
>> I have a long array (say 2xN, with N of the order of 10^5 at least) made
>> up of couples of numerical values.
>> I would like to sort these N couples in increasing order of the value of
>> the numbers in the lower row.
>> It is very easy to use sort() to take care of the sorting of the lower
>> row, but then I also have to sort the upper row so that the values of
>> each couple still match.
>> I did it using a double loop, but for large N this is very slow.
>> This is really a bottleneck in my code...
>> Any suggestions?
>> Regards
>>
>> Lorenzo
>>
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>
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