Textjoin: Using a unique ID, how do I concat multiple values?

Question

I\'m having trouble getting this to work. Basically, I have the following set of data:

In the TextJoin Formula column, I want it to do a look up against the

Answer 1

use:

=TEXTJOIN(",",TRUE,IF($A$2:$A$6=$A2,$B$2:$B$6,""))

Depending on one's version this may require Ctrl-Shift-Enter instead of Enter when exiting edit mode.

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If one has the Dynamic Array Formula FILTER:

=TEXTJOIN(",",,FILTER(B:B,A:A=A2))