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.
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