Examining R's Non-Standard Evaluation Behavior with subscramble

subscramble_nse.R

library(pryr)

sample_df <- data.frame(a = 1:5, b = 5:1, c = c(5, 3, 1, 4, 1))

scramble <- function(x) x[sample(nrow(x)), ]

subset1 <- function(x, cond) {
  condition_call <- substitute(cond)
  r <- eval(condition_call, x, parent.frame())
  x[r, ]
}

## Doesn't Work
subscramble1 <- function(x, condition) {
  scramble(subset1(x, condition))
}

## Works
subset2_q <- function(x, condition) {
  r <- eval(condition, x, parent.frame())
  x[r, ]
}

subset2 <- function(x, condition) {
  subset2_q(x, substitute(condition))
}

subscramble2 <- function(x, condition) {
  condition <- substitute(condition)
  scramble(subset2_q(x, condition))
}

subscramble1(sample_df, a >= 3)
subscramble2(sample_df, a >= 3)