Hi all,

A little background info: I'm a fisheries research technician and we are doing a fish movement study. I am also an excel novice.

I have data in three columns as follows:

Date I.D. Location
5/9/14 3 lake
6/18/14 3 stream 1
7/15/14 17 lake
8/21/14 17 stream 1
9/5/14 17 stream 2
5/26/14 50 stream 1
5/30/14 50 stream 2
7/21/14 50 stream 1

This data above comes from antenna arrays along a stream that are tracking movement of tagged fish (I.D.'s) from a lake to an adjoining stream to see how far up they go and when they are moving. "Stream 1" is the same as stream as "stream 2", "stream 2" just denotes a reach that is further upstream than "stream 1".

Anyway, I would like to arrange the data so that I can see the location of each fish on any given day in the season. I have a column of continuous dates in "column A" and a row of individual I.D.'s in "row 1" and need to fill this table with the info that I have in the format of the above example. The hard part is filling in the data from dates that are not included in my data already. For I.D. "3" the end result would have locations (lake, stream, or stream2) filled in for dates in May through September. For example, for fish I.D. "3", the dates 5/9/14 through 6/18/14 would have the location "lake", and all dates after that would have the location "stream 1". The only way I can figure how to do this is using vlookup for every single fish I.D. and that isn't very efficient (there are 1000's of fish I.D.'s). Any ideas on a more efficient way to do this?