find duplicates, combine differences

[eusair]

i have downloaded botanical indexes for multiple counties and i am trying to combine them. i want to compare the 'genus' and 'species' columns and if both are equal (they are the same plant), i would then like for the respective counties to be combined into a single cell.

for what it is worth, i have indexes for ~9 counties which is a list of plants ~7000 long. i suspect that once duplicates are removed, the list will be closer to 2500 individual species.

for example:

Genus	Species	County
Vicia	caroliniana	C
Vicia	caroliniana	Ch
Vicia	caroliniana	M
Vicia	caroliniana	S
Vicia	grandiflora	M
Vicia	grandiflora	S
Vicia	hirsuta	G
Vicia	hirsuta	S
Vicia	lathyroides	S
Vicia	minutiflora	C
Vicia	sativa	Ch
Vicia	sativa	M
Vicia	sativa	S
Vicia	tetrasperma	C
Vicia	tetrasperma	Ch
Vicia	tetrasperma	G
Vicia	tetrasperma	M
Vicia	villosa	Ch
Vicia	villosa	G
Vicia	villosa	M
Vicia	villosa	S

becomes

Genus	Species	County
Vicia	caroliniana	C, Ch, M, S
Vicia	grandiflora	M, S
Vicia	hirsuta	G, S
Vicia	lathyroides	S
Vicia	minutiflora	C
Vicia	sativa	Ch, M, S
Vicia	tetrasperma	C, Ch, G, M
Vicia	villosa	Ch, G, M, S

Many thanks for your help. Go Science!

[hoyasaxa215]

This can be easily done with the "=ARLOOKUP" UDF. See link below.

http://www.excelguide.eu/120/810/120/EN_ARLookUp.html

[hoyasaxa215]

Here's a sample file for your example. I had to create some helper columns for the lookup to work.

[eusair]

hey, that's fantastic! thank you, hoyasaxa. i'm glad you provided that attachment b/c i was just about to ask for a little extra help. but that made all the difference and i'm well on my way. thanks again!