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Two left-hand Selection from two listboxes that feed into one right-hand listbox?

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Two left-hand listboxes that feed into one right-hand listbox?

Has anyone seen a ux/ui pattern like the one below? (Examples?)

It is two left-hand listboxes that feed into one right-hand listbox.

Any suggestions for improvement? User experience concerns? Is there any other ui/ux pattern that you would suggest?

Notes:

  • Lists can be very large, up to ~1000.
  • Actual list items are more complex than "songs", but I need to be generic.
  • We discussed having one left-hand listbox and combining the items, denoting "my songs" with an indicator icon, but it caused confusion about what was supposed to be cleared when the user selects the search's clear button. Though - it is still an option if this design does not pan out.

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