[R] Need a faster function to replace missing data
mudiver1200 at yahoo.com
Fri May 22 06:45:26 CEST 2009
I need some help in coming up with a function that will take two data sets, determine if a value is missing in one, find a value in the second that was taken at about the same time, and substitute the second value in for where the first should have been. My problem is from a fish tracking study. We put acoustic tags in fish and track them for several days. Location data is supposed to be automatically recorded every time we detect a "ping" from the fish. Unfortunately the GPS had some problems and sometimes the fishes depth was recorded but not its location. I fortunately had a back-up GPS that was taking location data every five minutes. I would like to merge the two files, replacing the missing value in the vscan (automatic) file with the location from the garmin file. Since we were getting vscan records every 1-2 seconds and garmin records every 5 minutes, I need to find the right place in the vscan file to place the garmin record - i.e. the
closest in time, but not greater than 5 minutes. I have written a function that does this. However, it works with my test data but locks up my computer with my real data. I have several million vscan records and several thousand garmin records. Is there a better way to do this?
My function and test data:
minute.diff<-1/24/12 #Time diff is in days, so this is 5 minutes
for (k in 1:nrow(myvscan))
if ((min(abs(mygarmin$DateTime-myvscan$DateTime[k]))) < minute.diff )
I appreciate your help and advice.
Department of Zoology
University of Hawaii
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