Y must be a simple integer vector of length 2 or 3 whose elements are:
| [1] | a file tie number |
| [2] | a number specifying the position and number of components to be dropped. A positive value indicates that components are to be removed from the beginning of the file; a negative value indicates that components are to be removed from the end of the file |
| [3] | an optional passnumber which if omitted is assumed to be zero |
The shy result of a ⎕FDROP is a vector of the numbers of the dropped components. This is analogous to ⎕FAPPEND in that the result is potentially useful for updating some sort of dictionary:
cnos,←vec ⎕FAPPEND¨tie ⍝ Append index to dictionary cnos~←⎕FDROP tie,-⍴vec ⍝ Remove index from dict.
Note that the result vector, though potentially large, is generated only on request.
⎕FSIZE 1 1 21 5436 4294967295 ⎕FDROP 1 3 ⋄ ⎕FSIZE 1 4 21 5436 4294967295 ⎕FDROP 1 ¯2 ⋄ ⎕FSIZE 1 4 19 5436 4294967295