Drop

R←X↓Y

Y may be any array. X must be a simple scalar or vector of integers. If X is a scalar, it is treated as a one-element vector. If Y is a scalar, it is treated as an array whose shape is (⍴X)⍴1. After any scalar extensions, the shape of X must be less than or equal to the rank of Y. Any missing trailing items in X default to 0.

R is an array with the same rank as Y but with elements removed from the vectors along each of the axes of Y. For the Ith axis:

if X[I] is positive, all but the first X[I] elements of the vectors result
if X[I] is negative, all but the last X[I] elements of the vectors result

If the magnitude of X[I] exceeds the length of the Ith axis, the result is an empty array with zero length along that axis.

Examples

      4↓'OVERBOARD'
BOARD
 
      ¯5↓'OVERBOARD'
OVER
 
      ⍴10↓'OVERBOARD'
0
 
      M
ONE
FAT
FLY
      0 ¯2↓M
O
F
F
 
      ¯2 ¯1↓M
ON
      1↓M
FAT
FLY
      M3←2 3 4⍴⎕A
 
      1 1↓M3
QRST
UVWX
      ¯1 ¯1↓M3
ABCD
EFGH