# Load packages

# Core
library(tidyverse)
library(tidyquant)

Functions

When should you write a function

# For reproducible work
set.seed(1234)

# 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$b - min(df$a, na.rm = TRUE)) /
    (max(df$b, na.rm = TRUE) - min(df$a, na.rm = TRUE))
df$c <- (df$c - min(df$a, na.rm = TRUE)) /
    (max(df$c, na.rm = TRUE) - min(df$a, na.rm = TRUE))
df$d <- (df$d - min(df$a, na.rm = TRUE)) /
    (max(df$d, na.rm = TRUE) - min(df$a, na.rm = TRUE))

df
## # A tibble: 10 × 4
##        a       b       c      d
##    <dbl>   <dbl>   <dbl>  <dbl>
##  1 0.332 -0.198   0.233   1    
##  2 0.765 -0.413  -0.854  -0.431
##  3 1     -0.321  -0.766  -0.644
##  4 0      0.0267  0.800  -0.455
##  5 0.809  0.397  -1.21   -1.48 
##  6 0.831 -0.0457 -2.52   -1.06 
##  7 0.516 -0.212   1      -1.98 
##  8 0.524 -0.377  -1.78   -1.22 
##  9 0.519 -0.347  -0.0263 -0.267
## 10 0.424  1      -1.63   -0.423
rescale <- function(x) {
    
    # body
   x <- (x - min(x, 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)

df
## # A tibble: 10 × 4
##        a      b     c     d
##    <dbl>  <dbl> <dbl> <dbl>
##  1 0.332 0.153  0.782 1    
##  2 0.765 0      0.473 0.519
##  3 1     0.0651 0.498 0.448
##  4 0     0.311  0.943 0.511
##  5 0.809 0.573  0.373 0.168
##  6 0.831 0.260  0     0.308
##  7 0.516 0.143  1     0    
##  8 0.524 0.0255 0.210 0.256
##  9 0.519 0.0472 0.708 0.575
## 10 0.424 1      0.253 0.522

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 {
        stop("Value is negative, the function must stop")
        print(x)
    }
}    
 
3 %>% detect_sign()
## [1] 3
0 %>% detect_sign()
## [1] 0
# -1 %>% detect_sign

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, 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