Examples

   ⎕←data←?3 4⍴10
1 7 4 5
2 0 6 6
9 3 5 8

   +/R 1 +data
17 14 25

   +/[1] data
17 14 25

   ⍋R 1 +data
0 2 3 1
1 0 2 3
1 2 3 0

   ⍋[1] data
SYNTAX ERROR
   ⍋[1]data
  ∧

   gradea←{c←¯1↑⍴⍵ ⋄ j←c/c×⍳×/¯1↓⍴⍵ ⋄ (⍴⍵)⍴j-⍨⍋j,[0.5],⍵}
   gradea data
0 2 3 1
1 0 2 3
1 2 3 0

   gradeb←{↑ ⍋¨ ⊂[¯1+⍴⍴⍵] ⍵}
   gradeb data
0 2 3 1
1 0 2 3
1 2 3 0

   {⍵[⍋⍵]}R 1 +data
1 4 5 7
0 2 6 6
3 5 8 9

   {⍵[⍋⍵]}[1] data
SYNTAX ERROR
   {⍵[⍋⍵]}[1]data
  ∧

   avg←{(+⌿⍵)÷⊃(⍴⍵),1}

   avg R 1 +data
4.25 3.5 6.25

   avg[1] data
SYNTAX ERROR
   avg[1]data
  ∧

   avg R 2 +data
4 3.33333 5 6.33333

   avg R 0 +data
1 7 4 5
2 0 6 6
9 3 5 8