Programming

Hone your programming skillz

If/else statements

Structure:

if(condition) {
  #code to run if condition is true
} else if(second condition) {
  #other code to run if second true
} else {
  #finally, code to run if conditions false
}

Example:

x <- "hello"
if (!is.numeric(x)) {
    print("Numeric input is required")
} else {
  print(TRUE)
}

## [1] "Numeric input is required"

Loops

• Reduces the amount of typing (if we have a lot of code that is essentially the same)
• R offers several loops: for, while, repeat.

For loops

for(i in 1:2){
  print(i)  
}

## [1] 1
## [1] 2

library(ggplot2)
cols <- colnames(diamonds)
for(i in cols) {
  print(paste(i, ":", class(diamonds[, i])))
}

## [1] "carat : numeric"
## [1] "cut : ordered" "cut : factor" 
## [1] "color : ordered" "color : factor" 
## [1] "clarity : ordered" "clarity : factor" 
## [1] "depth : numeric"
## [1] "table : numeric"
## [1] "price : integer"
## [1] "x : numeric"
## [1] "y : numeric"
## [1] "z : numeric"

While loops

i <- 1
while (i <= 5) {
  print(i)
  i <- i + 1
}

## [1] 1
## [1] 2
## [1] 3
## [1] 4
## [1] 5

Write your own functions!

Example function

foo <- function(params) {
  #code goes here
  return(output)
}

Hello, world!

foo <- function(n = 10) {
  stopifnot(n > 0)
  for(i in 1:n){
    print("Hello, world \n")
  }
}
foo(3)

## [1] "Hello, world \n"
## [1] "Hello, world \n"
## [1] "Hello, world \n"