Intro

When should you write a function?

# Creat a data frame
set.seed(1234)

df <- tibble::tibble(
    a = rnorm(10),
    b = rnorm(10),
    c = rnorm(10), 
    d = rnorm(10)
)
# Resclae each colum

df$a <- (df$a - min(df$a, na.rm = TRUE)) /
    (max(df$a, na.rm = TRUE) - min(df$a, na.rm = TRUE))
df$b <- (df$b - min(df$b, na.rm = TRUE)) /
    (max(df$b, na.rm = TRUE) - min(df$b, na.rm = TRUE))
df$c <- (df$c - min(df$c, na.rm = TRUE)) /
    (max(df$c, na.rm = TRUE) - min(df$c, na.rm = TRUE))
df$d <- (df$d - min(df$d, na.rm = TRUE)) /
    (max(df$d, na.rm = TRUE) - min(df$d, na.rm = TRUE))
square <- function(var) {
    
    # body
    squared_value <- var * var
    
    #return value
    return(squared_value)
}
rescale <- function(x) {
    # Body
    x <- (x - min(df$a, na.rm = TRUE)) /
    (max(x, na.rm = TRUE) - min(x, na.rm = TRUE))
    
    # return values
    return(x)
    
    
}
df$a <- rescale (df$a)
df$b <- rescale (df$b)
df$c <- rescale (df$c)
df$d <- rescale (df$d)

Conditional execution

detect_sign <- function(x) {
    
    if(x > 0) {
        message("Value is positive")
    print(x)
    } else if(x == 0) {
        warning("Value is not positive, but it can be accepted")
        print(x)
    } else {
        stop("Value is negative, the fuction must stop")
        print(x)
    }
}

3 %>% detect_sign()
## Value is positive
## [1] 3
0 %>% detect_sign()
## Warning in detect_sign(.): Value is not positive, but it can be accepted
## [1] 0

Function arguments

?mean
x <- c(1:10, 100, NA)
x
##  [1]   1   2   3   4   5   6   7   8   9  10 100  NA
x %>% mean()
## [1] NA
x %>% mean(na.rm = TRUE)
## [1] 14.09091
x %>% mean(na.rm = TRUE, trim = 0.1)
## [1] 6
mean_remove_na <- function(x, na.rm = TRUE, ...) {
    
    avg <- mean(x, na.rm = na.rm, ...)
    
    return(avg)
}


x %>% mean_remove_na()
## [1] 14.09091
x %>% mean_remove_na(na.rm = FALSE)
## [1] NA
x %>% mean_remove_na(trim = 0.1)
## [1] 6

two types of functions