set variable from column value

[vvvvvvvvvv]

Table:

A B

A1 B1

A2 B2

A3 B3

How can I assign column B value to a variable if the corresponding columnA value equal 'A1'.
There are some analysis can get the number of count count({<A='A1'> B} 
But I need is not agg count. I need the whole value......

[Taoufiq_Zarra]

what is the expected output from this table ?

[vvvvvvvvvv]

Table:

A B

A1 B1

A2 B2

A3 B3

raw data is as above

I want is a value of columnB when columnA equal to 'A1'

[Taoufiq_Zarra · Accepted solution]

Maye be :

=Only({<A={'A1'}>} B)