How to create the expression for below requirement in Qlikview multibox

[Vamsy1991]

Source='Q1','Q2','Q3','Q4'

Target ='Q1','Q2','Q3','Q4'

If i selected Source='Q1' requirement is i need to show  Target='Q2','Q3','Q4' in dropdown except 'Q1' in Target

Same like Taget also

If i selected Target='Q1' requirement is i need to show  Source='Q2','Q3','Q4' in dropdown except 'Q1' in Source

I need different selections for Source and Target,Could you please help me

[edwin · Accepted solution]

Create a straight table chart
use Target as the dimension,
use the following as expression (totals off):

=sum({<Target-={'$(=only(Source))'}>}1)

this excludes the selected source.

in presentation, hide the expression so only dimension shows, disable caption, disable indicators, disable interactive sort.  this simulates a list box

do something similar to Source with expression 

=sum({<Source-={'$(=only(Target))'}>}1)

click Source and it will be selected, then target shows values of what werent selected.  this assumes only one will be selected.  if multiple selections are required, its a different formula in the exclusion set analysis