Apply a set of functions to an object

Question

I have a dataframe with a set of objects df$data and a set of rules to be applied on every object df$rules.

df <- data.frame(
  data = c(1,2,3),
  rules = c("rule1", "rule1, rule2, rule3", "rule3, rule2"),
  stringsAsFactors = FALSE
)

The rules are

rule1 <- function(data) {
  data * 2
}

rule2 <- function(data) {
  data + 1
}

rule3 <- function(data) {
  data ^ 3
}

For every row in the dataframe I want to apply all the rules specified in the rules column. The rules should be applied in series.

What I figured out:

apply_rules <- function(data, rules) {
  for (i in 1:length(data)) {
    rules_now <- unlist(strsplit(rules[i], ", "))
    for (j in 1:length(rules_now)) {
      data[i] <- apply_rule(data[i], rules_now[j])
    }
  }
  return(data)
}

apply_rule <- function(data, rule) {
  return(sapply(data, rule))
}


apply_rules(df$data, df$rules)
# [1]   2 125  28

Although this works I'm pretty sure there must be more elegant solutions. On SO I could find lot's of stuff about the apply-functions and also one post about applying many functions to a vector and something about chaining functions. The Compose idea looks promising but I couldn't figure out how to make a call to Compose with my rules as string. (parse() didn't work..)

Any hints?

Answer 1

Some good answers already but throw in another option - build a pipe chain as a string then evaluate it. For example - for row 1 - eval(parse(text = "1 %>% rule1")) gives 2

eval_chain <- function(df) {
    eval(parse(text = paste(c(df$data, unlist(strsplit(df$rules, ", "))), collapse=" %>% ")))
}

df$value <- sapply(1:nrow(df), function(i) df[i, ] %>% eval_chain)
  # data               rules value
# 1    1               rule1     2
# 2    2 rule1, rule2, rule3   125
# 3    3        rule3, rule2    28