disp ← { ⍵ ⊃¨ ((2↓⎕D),'TJQKA')('♣♢♡♠') }
      disp¨ ⍳13 4
 2♣  2♢  2♡  2♠
 3♣  3♢  3♡  3♠
 4♣  4♢  4♡  4♠
 5♣  5♢  5♡  5♠
 6♣  6♢  6♡  6♠
 7♣  7♢  7♡  7♠
 8♣  8♢  8♡  8♠
 9♣  9♢  9♡  9♠
 T♣  T♢  T♡  T♠
 J♣  J♢  J♡  J♠
 Q♣  Q♢  Q♡  Q♠
 K♣  K♢  K♡  K♠
 A♣  A♢  A♡  A♠

      disp ← ⊃¨ ∘ ((2↓⎕D),'TJQKA')('♣♢♡♠')

Pick (⊃) serves our purposes here, but later we'll need a function which selects major cells of the right argument using scalars from the left. Let's start using it now. I for index!

      I ← ⌷⍤0 99
      disp ← I¨ ∘ ((2↓⎕D),'TJQKA')('♣♢♡♠') ⍤ 1

The specification of rank 1 both ensures and documents that the inner function will only be called on vectors or scalars.