Creating functions within a nested loop

Question

I was hoping to create a function with the if statements in the following code:

data <- data.frame(
  id = c(1, 5, 6, 11, 15, 21),
  intervention = c(2, 2, 2, 1, 1, 1),
  death = c(0, 1, 0, 1, 0, 0)
)

test <- c()
for (i in data$id[which(data$intervention == 1)]) {
  print(paste0("id = ", i, ": "))
  for (j in data$id[which(data$intervention == 2)]) {
    if (data$death[data$id == i] < data$death[data$id == j]) {
      test <- c(test, -1)
    } else if (data$death[data$id == i] > data$death[data$id == j]) {
      test <- c(test, 1)
    } else if (data$death[data$id == i] == data$death[data$id == j]) {
      test <- c(test, 0)
    }
  }
  print(test)
  test <- c()
}

I had tried to do it as follows, however the code is not writing the result to the vector. However if I replaced the return with print, it would print it out. Would anyone have any suggestions on what I might be doing wrong? Many thanks!

first <- function () {
  if(data$death[data$id == i]<data$death[data$id ==j]){
   return (test <- c(test,-1))}
  else if(data$death[data$id == i]>data$death[data$id == j]){
   return (test <- c(test,1))}
  else if(data$death[data$id == i]==data$death[data$id == j]){
   return (test <- c(test,0))} 
}

for (i in data$id[which(data$intervention == 1)]){
  for (j in data$id[which(data$intervention == 2)]){ 
    first()
  }
test
}

you are not saving the output... it would have to look something like this: test<-first(). that is not your only problem. you aren't feeding your function any input but change the data frames outside your function. this makes your function very easy to break and 100% task dependent. that negates the whole point of creating a function. — D.J
– D.J, Commented Nov 22, 2022 at 5:40

Rui Barradas · Accepted Answer · 2022-11-22 06:13:43Z

1

The following function returns a list of the wanted vectors.

first <- function(data, interv1 = 1, interv2 = 2) {
  inx <- which(data[["intervention"]] == interv1)
  jnx <- which(data[["intervention"]] == interv2)
  out <- lapply(inx, \(i) {
    sapply(jnx, \(j) sign(data[["death"]][i] - data[["death"]][j]))
  })
  setNames(out, data[["id"]][inx])
}

first(data)
#> $`11`
#> [1] 1 0 1
#> 
#> $`15`
#> [1]  0 -1  0
#> 
#> $`21`
#> [1]  0 -1  0

^{Created on 2022-11-22 with reprex v2.0.2}

You can then access the return values as

test <- first(data)

# any of the following extracts the 1st vector
test[['11']]
#> [1] 1 0 1

# notice the backticks
test$`11`
#> [1] 1 0 1

^{Created on 2022-11-22 with reprex v2.0.2}

answered Nov 22, 2022 at 6:13

Rui Barradas

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