How to figure out that Stock A (for example) is held in both Portfolio 1 and 3

Many thanks in advance for any help in this matter!

I've attached my problem as an image.

I have three portfolios on the left, each containing a selection of stocks.

I've then organised this into a table, with a list of the unique stocks in one column, and the names of each portfolio in their own columns. What is the formula that I would need to type in that would figure out that Stock A (for example) is held in both Portfolio 1 and 3?

As an extra question, I currently plan on creating the list of unique stocks by copy & pasting the whole list, and then pressing the 'remove duplicates' button under the Data tab. This will be a pain to repeat every time I add a new portfolio with a new selection of stocks etc., so is there any way to automate that process as well?

Really appreciate any help on this.

Assuming that your table is in E and to right, then in F2, under Portofolio 1: =countifs($a:$a,f$1,$b:$b,$e2)
For totals in sum, =countif($b:$b,$e2)
For unique list in E2: =INDEX($b1:$b100,MATCH(0,COUNTIF($e$1:e1,$b1:$b100),0)), array entered using Ctrl+Shift+Enter

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