Answering my own question: if I explicitly garbage collecte before the
benchmark then 'index' always wins, which probably also answers the
original question.
v<-rep(1:1000,1:1000); x<-5; gc(); benchmark(replications=200,
columns=c("test","elapsed"), order="elapsed", which=length(which(x==v)),
index=length(v[v==x]), sum=sum(v==x))
Allan
On 19/06/09 16:51, Allan Engelhardt wrote:
> When trying out a couple of different approaches to this problem I get
> rather different answers between runs. Anybody know why?
>
> > library("rbenchmark")
> > v<-rep(1:1000,1:1000); x<-5; benchmark(replications=200,
> columns=c("test","elapsed"), order="elapsed",
> which=length(which(x==v)), index=length(v[v==x]), sum=sum(v==x))
> test elapsed
> 3 sum 2.513
> 2 index 5.512
> 1 which 6.712
> > v<-rep(1:1000,1:1000); x<-5; benchmark(replications=200,
> columns=c("test","elapsed"), order="elapsed",
> which=length(which(x==v)), index=length(v[v==x]), sum=sum(v==x))
> test elapsed
> 3 sum 2.502
> 2 index 3.779
> 1 which 6.650
> > v<-rep(1:1000,1:1000); x<-5; benchmark(replications=200,
> columns=c("test","elapsed"), order="elapsed",
> which=length(which(x==v)), index=length(v[v==x]), sum=sum(v==x))
> test elapsed
> 2 index 3.796
> 3 sum 5.808
> 1 which 6.633
>
> This pattern appears to repeat (so on the next two runs "sum" will win
> followed by "index" followed by "sum" twice followed by "index" ...)
>
> Allan.
>
>
>
>
> On 19/06/09 14:55, Praveen Surendran wrote:
>> Hi,
>>
>>
>>
>> I have a vector "v" and would like to find the number of occurrence of
>> element "x" in the same.
>>
>> Is there a way other than,
>>
>>
>>
>> sum(as.integer(v==x)) or length(which(x==v))
>>
>>
>>
>> to do the this.
>>
>>
>>
>> I have a huge file to process and do this. Both the above described
>> methods
>> are pretty slow while dealing with a large vector.
>>
>> Please have your comments.
>>
>>
>>
>> Praveen Surendran.
>>
>>
>>
>>
>> [[alternative HTML version deleted]]
>>
>> ______________________________________________
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>> PLEASE do read the posting guide
>> http://www.R-project.org/posting-guide.html
>> and provide commented, minimal, self-contained, reproducible code.
>>
>
> ______________________________________________
> R-help@r-project.org mailing list
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> PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
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