File Drop Component {R}←⎕FDROP Y

Access code 32

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.

Examples

      ⎕FSIZE 1
1 21 5436 4294967295

      ⎕FDROP 1 3 ⋄ ⎕FSIZE 1
4 21 5436 4294967295

      ⎕FDROP 1 ¯2 ⋄ ⎕FSIZE 1
4 19 5436 4294967295