Functions

Functions are something I love to hate. They can be extremely frustrating, but it's a good feeling when they work well. Our assignment this week was to write a simple function. I wrote one to assess the pass/fail rate on a test, and return the percentage of passing students. Below, I present my workthrough to the final product, which can be found on github HERE

First we need some data.

x <- rnorm(250,75,22)

250 students took a test, the average was a 75, and the standard deviation was 22.

I then wrote a simple function to assess show which students passed and which failed.

passfail <- function(x) {
  ifelse(x>=60,'pass','fail')
}

then I tested it out

passfail(x)
  [1] "pass" "pass" "pass" "pass" "fail" "fail" "fail" "pass" "fail" "pass" "fail" "pass" "fail" "pass"
 [15] "pass" "pass" "pass" "fail" "fail" "pass" "pass" "pass" "fail" "pass" "pass" "pass" "pass" "fail"
 [29] "fail" "pass" "pass" "pass" "pass" "fail" "pass" "fail" "fail" "pass" "pass" "pass" "fail" "fail"
 [43] "pass" "pass" "pass" "fail" "fail" "pass" "pass" "pass" "pass" "fail" "pass" "fail" "pass" "fail"
 [57] "fail" "fail" "pass" "pass" "pass" "pass" "pass" "fail" "pass" "pass" "pass" "pass" "pass" "pass"
 [71] "pass" "pass" "pass" "pass" "pass" "pass" "pass" "fail" "pass" "fail" "pass" "fail" "pass" "pass"
 [85] "fail" "fail" "pass" "pass" "pass" "pass" "pass" "pass" "pass" "fail" "pass" "fail" "pass" "pass"
 [99] "fail" "pass" "pass" "pass" "fail" "fail" "pass" "pass" "pass" "fail" "pass" "pass" "pass" "pass"
[113] "pass" "fail" "pass" "fail" "fail" "pass" "pass" "pass" "pass" "pass" "fail" "pass" "pass" "pass"
[127] "pass" "pass" "pass" "pass" "fail" "pass" "pass" "pass" "fail" "pass" "fail" "fail" "fail" "pass"
[141] "pass" "pass" "fail" "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass" "fail" "fail" "pass"
[155] "pass" "pass" "pass" "pass" "pass" "pass" "fail" "fail" "pass" "pass" "pass" "fail" "fail" "pass"
[169] "pass" "fail" "pass" "pass" "pass" "pass" "pass" "fail" "pass" "pass" "pass" "pass" "pass" "pass"
[183] "pass" "pass" "pass" "pass" "fail" "pass" "pass" "pass" "fail" "fail" "pass" "pass" "fail" "pass"
[197] "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass" "fail" "pass"
[211] "pass" "pass" "pass" "fail" "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass"
[225] "pass" "pass" "pass" "fail" "pass" "pass" "fail" "pass" "pass" "fail" "pass" "fail" "pass" "pass"
[239] "fail" "fail" "fail" "fail" "fail" "pass" "pass" "pass" "pass" "pass" "pass" "pass"

Cool! It worked. However when looking at examples I noticed a low of functions had this "return" function written within. Let's just do what everyone else does and incorporate it.

passfail <- function(x) {
 score <- ifelse(x>=60,'pass','fail')
 print("score")
 }
passfail(x)
[1] "score"

Oops! That's not what we want. Turns out "score" should not be parenthesized.

passfail <- function(x) {
  score <- ifelse(x>=60,'pass','fail')
  print(score)
}

passfail(x)
  [1] "pass" "pass" "pass" "pass" "fail" "fail" "fail" "pass" "fail" "pass" "fail" "pass" "fail" "pass"
 [15] "pass" "pass" "pass" "fail" "fail" "pass" "pass" "pass" "fail" "pass" "pass" "pass" "pass" "fail"
 [29] "fail" "pass" "pass" "pass" "pass" "fail" "pass" "fail" "fail" "pass" "pass" "pass" "fail" "fail"
 [43] "pass" "pass" "pass" "fail" "fail" "pass" "pass" "pass" "pass" "fail" "pass" "fail" "pass" "fail"
 [57] "fail" "fail" "pass" "pass" "pass" "pass" "pass" "fail" "pass" "pass" "pass" "pass" "pass" "pass"
 [71] "pass" "pass" "pass" "pass" "pass" "pass" "pass" "fail" "pass" "fail" "pass" "fail" "pass" "pass"
 [85] "fail" "fail" "pass" "pass" "pass" "pass" "pass" "pass" "pass" "fail" "pass" "fail" "pass" "pass"
 [99] "fail" "pass" "pass" "pass" "fail" "fail" "pass" "pass" "pass" "fail" "pass" "pass" "pass" "pass"
[113] "pass" "fail" "pass" "fail" "fail" "pass" "pass" "pass" "pass" "pass" "fail" "pass" "pass" "pass"
[127] "pass" "pass" "pass" "pass" "fail" "pass" "pass" "pass" "fail" "pass" "fail" "fail" "fail" "pass"
[141] "pass" "pass" "fail" "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass" "fail" "fail" "pass"
[155] "pass" "pass" "pass" "pass" "pass" "pass" "fail" "fail" "pass" "pass" "pass" "fail" "fail" "pass"
[169] "pass" "fail" "pass" "pass" "pass" "pass" "pass" "fail" "pass" "pass" "pass" "pass" "pass" "pass"
[183] "pass" "pass" "pass" "pass" "fail" "pass" "pass" "pass" "fail" "fail" "pass" "pass" "fail" "pass"
[197] "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass" "fail" "pass"
[211] "pass" "pass" "pass" "fail" "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass"
[225] "pass" "pass" "pass" "fail" "pass" "pass" "fail" "pass" "pass" "fail" "pass" "fail" "pass" "pass"
[239] "fail" "fail" "fail" "fail" "fail" "pass" "pass" "pass" "pass" "pass" "pass" "pass"

Working again, good. It's printing the argument of 'score' rather than the word score, which is what parenthesis made it do.

This by itself is good, but why not see what percentage actually passes. I worked "percentage" in as a returned argument as well;

passfail <- function(x) {
 score <- ifelse(x>=60,'pass','fail')
 percentages <- ((length(which(score=='pass')))/(length(score)))*100
 print(score)
 print(percentages)
 }

passfail(x)
  [1] "pass" "pass" "pass" "pass" "fail" "fail" "fail" "pass" "fail" "pass" "fail" "pass" "fail" "pass"
 [15] "pass" "pass" "pass" "fail" "fail" "pass" "pass" "pass" "fail" "pass" "pass" "pass" "pass" "fail"
 [29] "fail" "pass" "pass" "pass" "pass" "fail" "pass" "fail" "fail" "pass" "pass" "pass" "fail" "fail"
 [43] "pass" "pass" "pass" "fail" "fail" "pass" "pass" "pass" "pass" "fail" "pass" "fail" "pass" "fail"
 [57] "fail" "fail" "pass" "pass" "pass" "pass" "pass" "fail" "pass" "pass" "pass" "pass" "pass" "pass"
 [71] "pass" "pass" "pass" "pass" "pass" "pass" "pass" "fail" "pass" "fail" "pass" "fail" "pass" "pass"
 [85] "fail" "fail" "pass" "pass" "pass" "pass" "pass" "pass" "pass" "fail" "pass" "fail" "pass" "pass"
 [99] "fail" "pass" "pass" "pass" "fail" "fail" "pass" "pass" "pass" "fail" "pass" "pass" "pass" "pass"
[113] "pass" "fail" "pass" "fail" "fail" "pass" "pass" "pass" "pass" "pass" "fail" "pass" "pass" "pass"
[127] "pass" "pass" "pass" "pass" "fail" "pass" "pass" "pass" "fail" "pass" "fail" "fail" "fail" "pass"
[141] "pass" "pass" "fail" "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass" "fail" "fail" "pass"
[155] "pass" "pass" "pass" "pass" "pass" "pass" "fail" "fail" "pass" "pass" "pass" "fail" "fail" "pass"
[169] "pass" "fail" "pass" "pass" "pass" "pass" "pass" "fail" "pass" "pass" "pass" "pass" "pass" "pass"
[183] "pass" "pass" "pass" "pass" "fail" "pass" "pass" "pass" "fail" "fail" "pass" "pass" "fail" "pass"
[197] "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass" "fail" "pass"
[211] "pass" "pass" "pass" "fail" "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass"
[225] "pass" "pass" "pass" "fail" "pass" "pass" "fail" "pass" "pass" "fail" "pass" "fail" "pass" "pass"
[239] "fail" "fail" "fail" "fail" "fail" "pass" "pass" "pass" "pass" "pass" "pass" "pass"

[1] 72.8

We can now see the full list of individual passes and fails, and the percentage of student's who passed.

The way it is now is fine perhaps, but it's a bit general. 60 points might be a good cutoff for most tests out of 100 points, but maybe a professor gives a very difficult test in which only 40 points are needed to pass. This next step marks the final product, and has an additional element set by the user, "y", which tells the function how many points equals a "pass". Let's try it out.

passfail <- function(x, y) {
  score <- ifelse(x>=y,'pass','fail')
  percentages <- ((length(which(score=='pass')))/(length(score)))*100
  print(score)
  print(percentages)
}


passfail(x, 40)

  [1] "pass" "pass" "pass" "pass" "pass" "pass" "fail" "pass" "pass" "pass" "fail" "pass" "pass" "pass"
 [15] "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass"
 [29] "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass"
 [43] "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass"
 [57] "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass"
 [71] "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass"
 [85] "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass"
 [99] "pass" "pass" "pass" "pass" "pass" "pass" "pass" "fail" "pass" "pass" "pass" "pass" "pass" "pass"
[113] "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass"
[127] "pass" "pass" "pass" "pass" "pass" "pass" "fail" "pass" "pass" "pass" "pass" "pass" "pass" "pass"
[141] "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass"
[155] "pass" "pass" "pass" "pass" "pass" "fail" "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass"
[169] "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass"
[183] "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass"
[197] "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass" "fail" "fail" "pass" "pass" "pass" "pass"
[211] "pass" "pass" "pass" "pass" "fail" "pass" "pass" "pass" "pass" "pass" "pass" "fail" "pass" "pass"
[225] "pass" "pass" "pass" "pass" "pass" "pass" "fail" "pass" "pass" "pass" "pass" "pass" "pass" "pass"
[239] "fail" "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass" "pass"


[1] 95.6