How to concatenate a range of cells based on another column

Hi

I have a set of over 20,000 rows of data spread across multiple topics.

Sample data below

Topics	Datas	Merge
mankind	i am me
mankind	I am ok
mankind	I am yours
mankind	today is
mankind	work it out	i am meI am okI am yourstoday is
earth	this is great
earth	thanks for all
earth	this is great
earth
earth	this is great
people	they are what
people	who said that
people	lets do it
people	ok you are right

So I have 3 columns, Col1 contains topics, Col2 contains respective datas, Col3 is empty

What I want to accomplish is a formula that will check the range of topics and where the topic ends, it will concatenate all the corresponding data together. In my sample data, where the topic mankind ends, it should combine all the datas above.

Thanks

With data beginning in A2:

=IF(A3<>A2,TEXTJOIN(" ",,IF(A$2:A2=A2,B$2:B2,"")),"")

see file.

I just noticed a stray zero. Amend to:

=IF(A3<>A2,TEXTJOIN(" ",TRUE,IF(A$2:A2=A2,B$2:B2&"","")),"")

Attach a workbook showing the issue.

Hi I noticed the issue occurs when it sees a very long text. if you use below text, you will see the error:

Short text: Lorem Ipsum has been the industry's standard dummy text ever since the 1500.
Long text: Lorem Ipsum has been the industry's standard dummy text ever since the 1500s, when an unknown printer took a galley of type and scrambled it to make a type specimen book. It has survived not only five centuries, but also the leap into electronic typesetting, remaining essentially unchanged. It was popularised in the 1960s with the release of Letraset

Saw this from excel: If your TEXTJOIN function crosses the limit of 32,767 characters then it will return the ?#VALUE!? error.

Perhaps a method of joining text row by row and then selecting only the fully completed text as in:
1. Column D: =A2<>A3
2. Column E: =IF(A2=A1,C1&B2,B2)
3. Column C: =IF(D2,E2,"")
Note that columns D:E may be moved and/or hidden for aesthetic purposes.
Let us know if you have any questions.