inv.seq {sfsmisc}

Inverse seq() – Short Expression for Index Vector

Description

Compute a short expression for a given integer vector, typically an index, that can be expressed shortly, using : etc.

Usage

inv.seq(i)

Arguments

i

vector of (usually increasing) integers.

Value

a call (“the inside of an expression”) to be eval()ed to return the original i.

Author(s)

Martin Maechler, October 1995; more elegant implementation from Tony Plate.

See Also

rle for another kind of integer vector coding.

Examples

(rr <- inv.seq(i1 <- c(3:12, 20:24, 27, 30:33)))
eval(rr)
stopifnot(eval(rr) == i1)

e2 <- expression(c(20:13, 3:12, -1:-4, 27, 30:31))
(i2 <- eval(e2))
(r2 <- inv.seq(i2))
stopifnot(all.equal(r2, e2[[1]]))

## Had {mapply()} bug in this example:
ii <- c(1:3, 6:9, 11:16)
stopifnot(identical(ii, eval(inv.seq(ii))))