[datatable-help] Bigger table , smaller access time-how is this possible?

[Ashim Kapoor]

Dear all,

Please see my reproducible example below. My question is why does the 2nd
table,which is bigger have a smaller access time ?

> library(xtable)
> library(data.table)
data.table 1.7.2  For help type: help("data.table")
> start.size<-6e+5
>
> time.data.table<-list()
>
> for (i in 0:1){
+ n<-start.size*10^i
+ n1<-n/5000
+
my.data.table<-data.table(index=1:n,seriesname=rep(as.character(as.hexmode(1:n1)),each=5000),value=rnorm(n))
+ setkey(my.data.table,"seriesname")
+
time.data.table[[i+1]]<-system.time(my.data.table[J(as.character(as.hexmode(n1/4))),])
+ }

>
> rbind(time.data.table[[1]],time.data.table[[2]])
     user.self sys.self elapsed user.child sys.child
[1,]     0.008        0   0.008          0         0
[2,]     0.004        0   0.004          0         0
> time.data.table[[1]]
   user  system elapsed
  0.008   0.000   0.008
> time.data.table[[2]]
   user  system elapsed
  0.004   0.000   0.004
>

Many thanks,
Ashim
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