Merging multiple (n) cells into one cell
 

I have 2 columns of data:
A B
3 yes
40 no
20 no
25 yes
18 yes

I crated a function on column C with =IF(I2="yes",C2,"").
What I want to do is to check if B is true/false, and display value in
column A. But also display all the values (3, 25, 18) in one single cell (so
I dont have to type it).

Each time this would have n rows (variable) and can't get the concantenante
function to work within a range of cells.