Module 12 Code along 11

R for Data Science: Chapter 14

Introduction

When should you write the function

# Create a data frame
df <- tibble::tibble(
  a = rnorm(10),
  b = rnorm(10),
  c = rnorm(10),
  d = rnorm(10)
)

# Rescale each column

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))

df

## # A tibble: 10 × 4
##        a     b      c       d
##    <dbl> <dbl>  <dbl>   <dbl>
##  1 0.444 0.623 1      0.819  
##  2 0.363 0     0.482  1      
##  3 0.572 0.475 0      0.332  
##  4 0.390 0.255 0.231  0.555  
##  5 1     0.380 0.479  0      
##  6 0.774 0.619 0.0596 0.990  
##  7 0.354 0.659 0.625  0.707  
##  8 0.519 1     0.765  0.544  
##  9 0.361 0.491 0.367  0.00119
## 10 0     0.435 0.536  0.673

rescale <- function(x) {
    
    # Body
    x <- (x- min(x, na.rm = TRUE)) /
        (max(x, na.rm = TRUE) - min(x,na.rm = TRUE))
    
    # Return
    return(x)
}

df$a <- rescale(df$a)
df$b <- rescale(df$b)
df$c <- rescale(df$c)
df$d <- rescale(df$d)

df

## # A tibble: 10 × 4
##        a     b      c       d
##    <dbl> <dbl>  <dbl>   <dbl>
##  1 0.444 0.623 1      0.819  
##  2 0.363 0     0.482  1      
##  3 0.572 0.475 0      0.332  
##  4 0.390 0.255 0.231  0.555  
##  5 1     0.380 0.479  0      
##  6 0.774 0.619 0.0596 0.990  
##  7 0.354 0.659 0.625  0.707  
##  8 0.519 1     0.765  0.544  
##  9 0.361 0.491 0.367  0.00119
## 10 0     0.435 0.536  0.673

Functions are for humans and computers

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 {
        message("Value is negative, the function 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

-1 %>% detect_sign()

## Value is negative, the function must stop

## [1] -1

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

Return value