A New Week!

We aren’t computer scientists and that’s okay!

We make lots of mistakes. Mistakes are funny. You can laugh with us.

Let’s go, Simba, Pumbaa, and Timon!

1 Some built-in functions for numbers

Almost everthing in R is done through functions.

Here are some commonly used functions that work with numbers.

1.1 Numeric functions

abs(x) absolute value

sqrt(x) square root – x^(1/2), x**(1/2)

round(x, digits = n) round x to n decimal digits

log(x) natural logarithm (base e)

log10(x) common logarithm (base 10)

exp(x) exponentials e^x

1.2 Statistical functions

mean(x, na.rm = FALSE) mean of x

median(x) median of x

sd(x) standard deviation of x

quantile(x, probs) quantiles of x with probability

range(x) smallest to largest values

max(x) maximum

min(x) minimum

sum(x) summation

2 Write functions

One of the great strengths of R is user can write customized functions.

In general, if you find yourself doing a lot of cutting and pasting, that’s usually a good sign to write a function.

Functions are defined using the function() and are stored as R objects just like anything else.

# Basic structure of creating a function 
function_name <- function(arguments) {
         function body
 }

# A simple example: convert Fahrenheit to Celsius
f_to_c <- function(temp_F) {
  temp_C <- (temp_F - 32) * 5 / 9
  #return(temp_C),
}

# In R, the return value of a function is always the very last expression that is evaluated
print(f_to_c(32))

airquality %>% 
  mutate(temp_c = f_to_c(Temp))

2.1 Argument matching

R functions arguments can be matched by position or by name.

Position matching just means that R assigns the first value to the first argument, the second value to second argument.

obtain_math <- function(a, b){
  a*a + b
}

print(obtain_math(a = 1, b = 2)) # arguments matched by name

print(obtain_math(1, 2)) # arguments matched by position

print(obtain_math(2, 1))

2.2 Argument with a default value

We must provide the argument values in the obtain_match() function if defualt values are not available

obtain_math(a = 1) # what happen if the value of b is missing?

We can modify the function to avoid such error by providing default values for arguments

obtain_math_v1 <- function(a, b=2){
  a*a + b
}

obtain_math_v1(1)

2.3 Apply functions

You can create and use functions inside your script.

#create a function to convert a month to season
obtain_season <- function(month){
    case_when(month %in% c(12, 1, 2) ~ "winter",
              month %in% c(3, 4, 5) ~ "spring",
              month %in% c(6, 7, 8) ~ "summer",
              month %in% c(9, 10, 11) ~ "fall")
}

obtain_season(7)

#apply the obtain_season() function 
library(tidyverse)

airquality %>% 
  mutate(season = obtain_season(Month))

You can also save your functions in a different script and use them again and again.

# we created a obtain_season() function and saved it in the my_functions.R
source('./script/my_functions.R') #use source() to read R code
class(obtain_season)

airquality %>% 
  mutate(season = obtain_season(Month))

Exercise

Write a function using year, month and day to obtain weekday/weekend: obtain_weekend()

Apply the function on airquality dataset

3 Recap

Some built-in functions for numbers
Write functions