Operator to perform an expression by group / conditionally on a factor / given a condition

by.R

`%|%` <- function(expr, group) {
  group <- as.factor(group)

  q   <- rlang::enquo(expr)
  exx <- rlang::quo_get_expr(q)
  evv <- rlang::quo_get_env(q)

  glb         <- codetools::findGlobals(as.function(list(exx)))
  gets        <- lapply(glb, get, envir = evv)
  names(gets) <- glb

  recss <- function(o, ss) {
    # recursive subset
    if (inherits(o, "data.frame")) return(subset(o, ss))
    if (is.vector(o) && length(o) == length(ss)) return(subset(o, ss))
    if (is.list(o)) return(lapply(o, recss, ss = ss))
    return(o)
  }

  v <- logical(length(group))
  for (i in levels(group)) {
    subenv <- recss(gets, group == i)
    v[group == i] <- eval(exx, subenv)
  }

  return(v)
}


# example: outlier detection by group
message("  %|% operator loaded. Usage:\n  (abs(mtcars$mpg - mean(mtcars$mpg)) > var(mtcars$mpg)) %|% mtcars$cyl")

source("https://gist.githubusercontent.com/vankesteren/2c1c7455e46209b72d478f397108abef/raw/11d95982894f42dc925a9da7e73ff1eefa1b3a7c/by.R")