Dynamically evaluate stored conditions

condition.r

# evaluate a condition
cond = function(expr, d=parent.frame()) {
  Reduce(`&`, lapply(expr, eval, d))
}


# example
l = list(
  'Condition 1'=expression(x > 0),
  'Condition 2'=expression(y < 0)
)

set.seed(1)
d = data.frame(
  x=trunc(runif(100, -10, 10)),
  y=trunc(runif(100, -10, 10))
)

b = d$x > 0 & d$y < 0
identical(b, with(d, cond(l)))
identical(b, cond(l, d))
identical(d[b, ], subset(d, cond(l)))