SAVOR: Part I

R brush-up

RStudio project setup

0. Start by opening RStudio and create a new project

Functions

1. Print function
   Let’s start by writing a function that will print its one argument (e.g. 2).

Code

myprint <- function(x) {
    print(x)
}

Code

myprint(2)

[1] 2

2. Default arguments Let’s now add a default value to this function’s argument

Code

myprint()

Error in myprint(): argument "x" is missing, with no default

Code

myprint_def <- function(x = "no name") {
    print(x)
}
myprint_def()

[1] "no name"

Control structures

3. for loop
   Now consider the following data.frame:

first_name	last_name	gender
Hermione	Granger	female
Ron	Weasley	male
Harry	Potter	male

Write a function that takes such a data.frame as a argument and that will print the last name for each row.

Code

print_last_name <- function(x) {
    for (i in 1:nrow(x)) {
        print(as.character(x[i, "last_name"]))
    }
}
print_last_name(hp_df)

[1] "Granger"
[1] "Weasley"
[1] "Potter"

4. while statement
   Now write the same function using a while statement.

Code

print_last_name_while <- function(x) {
    i <- 1
    while (i <= nrow(x)) {
        print(as.character(x[i, "last_name"]))
        i <- i + 1
    }
}
print_last_name_while(hp_df)

[1] "Granger"
[1] "Weasley"
[1] "Potter"

5. if/else statement
   Finally, write a function that will print the last name for females and the first name for males.

Code

print_last_name_if <- function(x) {
    for (i in 1:nrow(x)) {
        if (x[i, "gender"] == "female") {
            print(as.character(x[i, "last_name"]))
        } else if (x[i, "gender"] == "male") {
            print(as.character(x[i, "first_name"]))
        }

    }
}
print_last_name_if(hp_df)

[1] "Granger"
[1] "Ron"
[1] "Harry"

There are only two hard things in Computer Science:

• cache invalidation, and
• naming things.

– Phil Karlton