I have a variable in lines which is "vendor" and i am looping through it but i want to see if a vendor name is repeating in the line it must not print i just wanna know how to compare

right now its like 

<t t-foreach="docs" t-as="o">
   <tr class="row2">
                                      <t t-set="i" t-value="o.vendor"/>

i know how to put a t-if condition but just help me with the condition. Thank you so much