[R] Resampling physiological data using R?

[tsunhin wong]

Dear all R users,

I am going to use R to process some of my physiological data about eye.

The problem is the recording machine does not sample in a reliably
constant rate: the time intervals between data sampled can vary from
9msec to ~120msec, while most around in the 15-30msec range.
The below is a fraction of a single data file of a trial:

Time	CursorX	CursorY	Pupilsize
1811543	-1	-1	-1
1811563	-1	-1	-1
1811584	511	370	4.175665
1811603	511	368	4.181973
1811624	521	368	4.210732
1811644	512	377	4.149632
1811664	524	377	4.275845
1811684	518	368	4.236212
1811703	516	370	4.238384
1811725	507	364	4.181157
1811744	509	371	4.185016
1811764	509	377	4.231987
1811784	514	387	4.252449
1811802	515	388	4.273726

My goal is to "resample" these data so that the "Time" column
increments by a regular interval, and the other columns of data are
the averages (or estimates) at the point in time according to
available data points.
I have done something that I use a regular interval that is larger
than the naturally occurring record machine, i.e. > 120msec for
example, and acquire an average of the available data points for any
particular regular time interval.

Now, I need to achieve resampling for smaller regular interval: i.e.
5msec intervals, and interpolate / intrapolate the missing data points
from the available ones.
i.e. I may have to split up data points into the number of the regular
intervals that it may occupied in time.

Do you know if there is any package that is doing something similar?
And because of the size of the data and computational demand (1500
files each with 2000-8000+ lines), can you suggest me some
(algorithmically) more efficient way of doing this?

Thanks a lot!

Regards,

      John