operator to check if floats are in sets of other floats, for R

float_matching.R

# for more info on comparing floats, this blog post is very informative: https://bitbashing.io/comparing-floats.html
# for more info on how floating point mathematics compares to "real" mathematics, see https://www.tandfonline.com/doi/full/10.1080/10724117.2019.1611061 

# helper function for approximate equality between floats
approx_equal <- function(a, b, tol = sqrt(.Machine$double.eps)) {
  abs(a - b) <= tol
}

# use instead of the %in% operator to check if floats are in sets of other floats
`%in_approx%` <- function(x, table) {
  matches <- vapply(X = x, FUN = function(i) {
    return(any(approx_equal(i, table)))
  }, FUN.VALUE = logical(1))
  return(matches)
}

# test below. standard comparisons "fail", %in_approx% gets what we want
table <- c(0.95,0.96,0.97)
x <- sample(x = seq(from=0.9,to=1,by=0.01),size = 20,replace = T)

x %in% table
x[x %in% table]

x %in_approx% table
x[x %in_approx% table]