[R] Testing if all elements are equal in a vector/matrix
baptiste auguie
baptiste.auguie at gmail.com
Tue Jun 16 14:58:03 CEST 2009
utkarshsinghal wrote:
> Hi Jim,
>
> What you are saying is correct. Although, my computer might not have
> same speed and I am getting the following for 10M entries:
>
> user system elapsed
> 0.559 0.038 0.607
>
> Moreover, in the case of character vectors, it gets more than double.
>
> In my modeling, which is already highly time consuming, I need to do
> check this for few thousand vectors and the entries can easily be 10M in
> each vector. So I am just looking for any possibilities of time saving.
> I am pretty sure that whenever elements are not all equal, it can be
> concluded from any few entries (most of the times). It will be worth if
> I can find a way which stops checking further the moment it find two
> distinct elements.
>
*very* naively, you could define a tunable length to test only the first
few lines of each vector first. It's probably only useful if you have a
good guess on the likelihood of non-identity within the first n entries,
testTwoStages <- function(x= 1:10, y= rep(1,100), head.stop = 3){
if(!isTRUE(all(head(x, head.stop) == head(y, head.stop))))
{
print(paste("quick test returned FALSE"))
return(FALSE)
} else {
print(paste("full test returned FALSE"))
return(identical(tail(x, length(x) - head.stop), tail(y, length(y) -
head.stop)))}
}
x <- seq(1, 1e6)
y <- x
y[325] <- 0
> system.time(testTwoStages(x, y))
[1] "full test returned FALSE"
user system elapsed
0.128 0.072 0.204
> system.time(testTwoStages(x, y, 400))
[1] "quick test returned FALSE"
user system elapsed
0.006 0.001 0.008
HTH,
baptiste
> Regards
> Utkarsh
>
>
> jim holtman wrote:
>
>> Just check that the first (or any other element) is equal to all the rest:
>>
>>
>>> x = c(1,2,rep(1,10000000)) # 10,000,000
>>> system.time(print(all(x[1] == x)))
>>>
>> [1] FALSE
>> user system elapsed
>> 0.18 0.00 0.19
>>
>>
>> This was for 10M entries.
>>
>> On Tue, Jun 16, 2009 at 7:42 AM, utkarshsinghal
>> <utkarsh.singhal at global-analytics.com
>> <mailto:utkarsh.singhal at global-analytics.com>> wrote:
>>
>>
>> Hi All,
>>
>> There are several replies to the question below, but I think there
>> must
>> exist a better way of doing so.
>> I just want to check whether all the elements of a vector are same. My
>> vector has one million elements and it is highly likely that there are
>> distinct elements in the first few itself. For example:
>>
>> > x = c(1,2,rep(1,100000))
>>
>> I want the answer as FALSE, which is clear from the first two
>> observations itself and we don't need to check for the rest.
>>
>> Does anybody know the most efficient way of doing this?
>>
>> Regards
>> Utkarsh
>>
>>
>>
>> From: Francisco J. Zagmutt <gerifalte28_at_hotmail.com
>> <http://gerifalte28_at_hotmail.com/>
>> <mailto:gerifalte28_at_hotmail.com
>> <mailto:gerifalte28_at_hotmail.com>?Subject=Re:%20%5BR%5D%20Testing%20if%20all%20elements%20are%20equal%20in%20a%20vector/matrix>>
>>
>> Date: Tue 30 Aug 2005 - 06:05:20 EST
>>
>>
>> Hi Doran
>>
>> The documentation for isTRUE reads 'isTRUE(x)' is an abbreviation of
>> 'identical(TRUE,x)' so actually Vincent's solutions is "cleaner" than
>> using identical :)
>>
>> Cheers
>>
>> Francisco
>>
>> />From: "Doran, Harold" <HDoran at air.org <mailto:HDoran at air.org>> /
>> />To: <vincent.goulet at act.ulaval.ca
>> <mailto:vincent.goulet at act.ulaval.ca>>, <r-help at stat.math.ethz.ch
>> <mailto:r-help at stat.math.ethz.ch>> /
>> />Subject: Re: [R] Testing if all elements are equal in a
>> vector/matrix /
>> />Date: Mon, 29 Aug 2005 15:49:20 -0400 /
>> /> /
>> >See ?identical
>> <http://tolstoy.newcastle.edu.au/R/help/05/08/11201.html#11202qlink1>
>> /> /
>> />-----Original Message----- /
>> />From: r-help-bounces at stat.math.ethz.ch
>> <mailto:r-help-bounces at stat.math.ethz.ch> /
>> />[mailto:r-help-bounces at stat.math.ethz.ch
>> <mailto:r-help-bounces at stat.math.ethz.ch>] On Behalf Of Vincent
>> Goulet /
>> />Sent: Monday, August 29, 2005 3:35 PM /
>> />To: r-help at stat.math.ethz.ch <mailto:r-help at stat.math.ethz.ch> /
>> />Subject: [R] Testing if all elements are equal in a vector/matrix /
>> /> /
>> /> /
>> />Is there a canonical way to check if all elements of a vector or
>> matrix are /
>> />the same? Solutions below work, but look hackish to me. /
>> /> /
>> /> > x <- rep(1, 10) /
>> /> > all(x == x[1]) # == operator does not provide for small
>> differences /
>> */>[1] TRUE /
>> */> > isTRUE(all.equal(x, rep(x[1], length(x)))) # ugly /
>> */>[1] TRUE /
>> */> /
>> />Best, /
>> /> /
>> />Vincent /
>> />-- /
>> /> Vincent Goulet, Associate Professor /
>> /> École d'actuariat /
>> /> Université Laval, Québec /
>> /> Vincent.Goulet_at_act.ulaval.ca
>> <http://vincent.goulet_at_act.ulaval.ca/>
>> <mailto:Vincent.Goulet_at_act.ulaval.ca
>> <mailto:Vincent.Goulet_at_act.ulaval.ca>?Subject=Re:%20%5BR%5D%20Testing%20if%20all%20elements%20are%20equal%20in%20a%20vector/matrix>
>> http://vgoulet.act.ulaval.ca <http://vgoulet.act.ulaval.ca/> /
>> /> /
>> />______________________________________________ /
>> />R-help at stat.math.ethz.ch <mailto:R-help at stat.math.ethz.ch>
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>> />R-help at stat.math.ethz.ch <mailto:R-help at stat.math.ethz.ch>
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>>
>>
>> ______________________________________________
>> R-help at r-project.org <mailto:R-help at r-project.org> mailing list
>> https://stat.ethz.ch/mailman/listinfo/r-help
>> PLEASE do read the posting guide
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>> <http://www.r-project.org/posting-guide.html>
>> and provide commented, minimal, self-contained, reproducible code.
>>
>>
>>
>>
>> --
>> Jim Holtman
>> Cincinnati, OH
>> +1 513 646 9390
>>
>> What is the problem that you are trying to solve?
>>
>
>
> [[alternative HTML version deleted]]
>
>
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--
_____________________________
Baptiste Auguié
School of Physics
University of Exeter
Stocker Road,
Exeter, Devon,
EX4 4QL, UK
Phone: +44 1392 264187
http://newton.ex.ac.uk/research/emag
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