Utilities: Imitate Primitives Index   <<   >>

 
   sort  ← {(⊂⍋⍵)⌷⍵}
   group ← {(1,2≠/sort i)⊂⍋i←⍳⍨⍵}

   group 'Mississippi'
┌─┬────────┬───────┬───┐
│0│1 4 7 10│2 3 5 6│8 9│
└─┴────────┴───────┴───┘

   iself  ← {⍳⍨ ⊂[1↓⍳⍴⍴⍵]⍵}
   group1 ← {(1,2≠/sort i)⊂⍋i←iself ⍵}

   t←'IBM' 'AAPL' 'GOOG' 'GOOG' 'AAPL' 
   ⎕←x←↑t,'MSFT' 'IBM' 'AAPL' 'AAPL' 'IBM'
IBM 
AAPL
GOOG
GOOG
AAPL
MSFT
IBM 
AAPL
AAPL
IBM 
   group1 x
┌─────┬───────┬───┬─┐
│0 6 9│1 4 7 8│2 3│5│
└─────┴───────┴───┴─┘

   group2 ← ⊂⍯  ⍝ v14.0