count the number of sequential duplicates excel

count the number of sequential duplicates excel

I have a listing of video conference calls in an excel spreadsheet.
The data rows are grouped into calls which all dialed the same dial in number.  The first column is something like:

6024 
6024 
6024 
6184 
6184 
6432 
6432 
6432

So the first three entries are people all talking to each other in one video conference, using the dial in number of 6024.  
The next two numbers is a 2 person video conference, and so on.
I want to count the number of participants who dialled into each dial in number.  I want to find out the distribution of meeting sizes.  To do this, I want to count the number of identical dial in numbers that occur in next to each other.
Note that dial in numbers are recycled, and can be used by different participants on other days, so I can't use a COUNTIF() function over the entire data range, as it will count duplicate dial in numbers occuring at different times.
I can only count duplicates that occur up until a different dial in number occurs.
How could I insert the number of participants in column B next to the last participant, so that I have:

6024 
6024 
6024 3 
6184 
6184 2
6432 
6432 
6432 3

Solutions/Answers:

Answer 1:

Assuming A is your called numbers column, then put “1” in B1

Then in B2 put

=IF(A2=A1,B1+1,1)

And drag it down. This will result in

6024    1
6024    2
6024    3
6184    1
6184    2
6432    1
6432    2
6432    3

So the highest number is the number of participants.

If you want to get rid of the counts, you can put this into C and it will populate the final count only.

Related:  TEXTJOIN() on an array incorrectly returns a blank
=IF(A1<>A2,B1,"")


6024    1   
6024    2   
6024    3   3
6184    1   
6184    2   2
6432    1   
6432    2   
6432    3   3

You can hide column B if it is distracting.

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