Hi Stacy,
To start simple, a loop is written as follows in R:
For (i in 1 : x){ }
If by ranking, you mean ordering data, than you can use package chron to create
time objects that are to my opinion practical to use.
If by ranking you meant classifying your data in function of tide classes,
In order to glue tide height (or tide current) onto each fish position
observation:
1: Convert dates times to POSIXct (do it all in GMT to avoid DST issues!).
2: Consider using NOAA tide data, available as 6 minute interval time
series http://tidesandcurrents.noaa.gov/api/ . Luke Miller has
