tasks a-s

Task/Scope-modifiers/R/scope-modifiers-5.r

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+d <- data.frame(a=c(2,4,6), b = c(5,7,9))
+also <- c(1, 0, 2)
+with(d, mean(b - a + also)) #returns 4
+
+## with() is built in, but you might have implemented it like this:
+
+with.impl <- function(env, expr) {
+  env <- as.environment(env)
+  parent.env(env) <- parent.frame()
+  eval(substitute(expr), envir=env)
+}
+with.impl(d, mean(b - a + also))