[R] Subset and order

[Rui Barradas]

Hello,

If time is one of the problems, precompute an ordered index, and use it 
every time you want the df sorted. But that would mean you can't do it 
in a single operation.

iord <- order(x$a)
subset(x[iord, ], b == 3)


Rui Barradas

Em 05-07-2013 20:47, Noah Silverman escreveu:
> That would work, but is painfully slow.  It forces a new sort of the data with every query.  I have 200,000 rows and need almost a hundred queries.
>
> Thanks,
>
> -N
>
>
> On Jul 5, 2013, at 12:43 PM, Rui Barradas <ruipbarradas at sapo.pt> wrote:
>
>> Hello,
>>
>> Maybe like this?
>>
>> subset(x[order(x$a), ], b == 3)
>>
>>
>> Hope this helps,
>>
>> Rui Barradas
>>
>> Em 05-07-2013 20:33, Noah Silverman escreveu:
>>> Hello,
>>>
>>> I have a data frame with several columns.
>>>
>>> I'd like to select some subset *and* order by another field at the same time.
>>>
>>> Example:
>>>
>>> a	b	c
>>> 1	2	3
>>> 3	3	4
>>> 2	4	5
>>> 1	3	4
>>> etc…
>>>
>>>
>>> I want to select all rows where b=3 and then order by a.
>>>
>>> To subset is easy:  x[x$b==3,]
>>> To order is easy: x[order(x$a),]
>>>
>>> Is there a way to do both in a single efficient statement?
>>>
>>> Thanks,
>>>
>>>
>>>
>>> --
>>> Noah Silverman, M.S., C.Phil
>>> UCLA Department of Statistics
>>> 8117 Math Sciences Building
>>> Los Angeles, CA 90095
>>>
>>>
>>>
>>>
>>> 	[[alternative HTML version deleted]]
>>>
>>>
>>>
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>