separate_steps.R

separate_steps.R

#' Convert a dplyr expression to a list of step objects
separate_steps <- function(expr, iscall=FALSE) {
  if (iscall) {
    call <- expr
  } else {
    call <- match.call()[["expr"]]
  }
  
  len <- length(call)
  if (len == 1) {
    # base case: original data
    ret <- list(data = call, value = eval(call))
    class(ret) <- "data"
    return(list(ret))
  } else if (len == 3) {
    if (deparse(call[[1]]) != "%>%") {
      stop(paste("Can process only expressions made up of %>% operations,",
                 "not", deparse(call[[1]])))
    }
    ret <- list(call = call[[3]], step = call[[3]][[1]],
                argexpr = as.list(call[[3]][-1]), value = eval(call))
    ret$argument <- paste(lapply(ret$argexpr, deparse), collapse = ", ")
    
    class(ret) <- "step"
    before <- separate_steps(call[[2]], TRUE)
    return(c(before, list(ret)))
  } else {
    stop(paste("Cannot parse call of length", len))
  }
}