How about starting your time from 1 instead of 0 to make indexing earier
(you can always substract one later).  If so:

> x
  time events
1    1      1
2    2     30
3    6     14
4   11      4
> y <- data.frame(time=seq(max(x$time)), events=rep(0, max(x$time)))
> y
   time events
1     1      0
2     2      0
3     3      0
4     4      0
5     5      0
6     6      0
7     7      0
8     8      0
9     9      0
10   10      0
11   11      0
> y$events[x$time] <- x$events
> y
   time events
1     1      1
2     2     30
3     3      0
4     4      0
5     5      0
6     6     14
7     7      0
8     8      0
9     9      0
10   10      0
11   11      4
>



On 5/30/06, Pete Cap <peteoutside@yahoo.com> wrote:
>
> Hello List,
>
> I am working on creating periodograms from IP network traffic logs using
> the Fast Fourier Transform.  The FFT requires all the data points to be
> evenly-spaced in the time domain (constant delta-T), so I have a step where
> I zero-pad the data.
>
> Lately I've been wondering if there is a faster way to do this.  Here's
> what I've got:
>
> * data1 is a data frame consisting of a timestamp, in seconds, from the
> beginning of the network log, and the number of network events that fell on
> that timestamp.
> Example:
> time,events
> 0,1
> 1,30
> 5,14
> 10,4
>
> *data2 is the zero-padded data frame.  It has length equal to the greatest
> value of "time" in data2:
> time,events
> 1,0
> 2,0
> 3,0
> 4,0
> 5,0
> 6,0
> 7,0
> 8,0
> 9,0
> 10,0
>
> So I run this for loop:
> for(i in 1:length(data1[,1])) {
>     data2[data1[i,1],2]<-data1[i,2]
> }
>
> Which goes to each row in data1, reads the timestamp, and writes the
> "events" to the corresponding row in data2.  The result is:
> time,events
> 0,1
> 1,30
> 2,0
> 3,0
> 4,0
> 5,14
> 6,0
> 7,0
> 9,0
> 9,0
> 10,4
>
> For a 24-hour log (86,400 seconds) this can take a while...Any advice on
> how to speed it up would be appreciated.
>
> Thanks,
> Pete Cap
>
>
> ---------------------------------
>
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-- 
Jim Holtman
Cincinnati, OH
+1 513 646 9390 (Cell)
+1 513 247 0281 (Home)

What is the problem you are trying to solve?

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