with.r

with(x, {
  f(z)
})

# Which of the following statements is this equivalent to?
#
#   a) x$f(x$z)
#   b) f(x$z)
#   c) x$f(z)
#   d) f(z)
#
# Scroll down for the answer






























# It depends on what's in x!

x <- list()
f <- function(x) x + 1
z <- 1

with(x, {
  f(z)
})

x <- list(x = 2)
with(x, {
  f(z)
})

x <- list(f = function(x) x + 10)
with(x, {
  f(z)
})

x <- list(f = function(x) x + 10, z = 10)
with(x, {
  f(z)
})


# This is one reason not to use with - you need to know 
# exactly what's in x before you can reason about the 
# result of the code