Problem with dedupe function

[Smithkin]

I have an 2013 spreadsheet with multiple columns of data and duplicate organisation names in column A. I have filtered some of the columns and then deduped column A to see how many organisations possessed the features that I had filtered on. I have found that if following filtering only one instance of an organisation name remains in column A, in some cases that instance can be removed during the dedupe though not in every case.
I have done a lot of worksheets and only noticed this on the last one - aghh!
What is logic for the dedupe that this occurs? What should I do to achieve the outcome that I want.
thanks for your time
Andrea

[pjwhitfield]

Sorry are you saying that when carrying out a dedupe then sometimes the results arent correct? ie there are instances youve found that the results dont contain some items at all?

ie
A
A
B
A
B
B
C
D
D


obviously should give
A
B
C
D

but are you saying that in some instances C may not appear in the results?

[FDibbins]

Instead of using Remove Duplicates, I would probably use a formula in a helper column to ID unique instances, and then use that in the filter

[Smithkin]

Hi, Yes, that's exactly what has happened. I wondered if it is to do with the filtering on other columns that I perfomed before carrying out the dedupe. So that the dedupe is retaining an instance of C that I can't see anymore because I ave filtered it out and getting rid of the instance of C that I can still see.

[Smithkin]

Thanks for the response. That's above my Excel knowledge, but I think I have seen some tutorials on this so will take a look at them.