Functions

1. Write a function called mystring that takes a vector as an argument and returns the first three characters from the string. Test it on words[1:10].

library(stringr)
mystring <- function(x) {
  str_sub(x, 1, 3)
}
mystring(words[1:10])

 [1] "a"   "abl" "abo" "abs" "acc" "acc" "ach" "acr" "act" "act"

2. Add an argument to mystring() that allows the user to control how many of the first characters should be returned. Test it on words[1:10] with 5 characters.

mystring <- function(x, chars) {
  str_sub(x, 1, chars)
}
mystring(words[1:10], chars = 5)

 [1] "a"     "able"  "about" "absol" "accep" "accou" "achie" "acros" "act"  
[10] "activ"

3. Set the default number of characters returned by mystring() to be 3 and test that the default works and that you can override the default.

mystring <- function(x, chars = 3) {
  str_sub(x, 1, chars)
}
mystring(words[1:10])

 [1] "a"   "abl" "abo" "abs" "acc" "acc" "ach" "acr" "act" "act"

mystring(words[1:10], chars = 5)

 [1] "a"     "able"  "about" "absol" "accep" "accou" "achie" "acros" "act"  
[10] "activ"

4. Add a step that checks whether the inputted vector is a character string. If it is, continue to return the truncated strings. If the vector is not a character string, use the stop() function to stop the computation and return a message to the console telling the user that the vector was not a character vector. Test your function with a character vector, a numeric vector, and a logical vector.

mystring <- function(x, chars = 3) {
  if (!is.character(x)) {
    stop("Please enter a character vector.")
  } else {
  str_sub(x, 1, chars)
  }
}

mystring(words[1:10])

 [1] "a"   "abl" "abo" "abs" "acc" "acc" "ach" "acr" "act" "act"

# mystring(1:10)
# mystring(c(TRUE, FALSE))

5. Create a function called parse_my_vector that does the following:

• Allows users to input a vector and a response to the argument type that determines whether the vector is a numeric ("num"), character ("char"), or logical ("logical") vector. There should be no default value. If the user response does not match any of these three strings, stop with a message asking the user to specify one of the three strings.
• For each type, checks whether the vector is actually the type specified by the user and stops with a message if they do not match.
• For numeric vectors, multiplies by 10. For character vectors, extracts the first three characters. For logical vectors, returns the number of TRUE responses.
• Before returning output, prints a message thanking the user.
• Returns the original vector and output of the functions described above.

parse_my_vector <- function(x, type) {
  if (type == "num") {
    if (is.numeric(x)) {
      output <- x / 10
    } else {
      stop("Type response does not match vector type.")
    }
  } else if (type == "char") {
    if (is.character(x)) {
      output <- str_sub(x, 1, 3)
    } else {
      stop("Type response does not match vector type.")
    }
  } else if (type == "logical") {
    output <- sum(x)
  } else {
    stop("Please enter either 'num', 'char', or 'logical'.")
  }
  message("Thank you!")
  list(x,output)
}

6. Check the following with parse_my_vector():

• x = 1:10, type = “num”
• x = 1:10, type = “char”
• x = words[1:10], type = “num”
• x = words[1:10], type = “char”
• x = c(TRUE, FALSE, TRUE), type = “num”
• x = c(TRUE, FALSE, TRUE), type = “logical”
• x = 1:10, type = “nums”

parse_my_vector(x = 1:10, type = "num")

Thank you!

[[1]]
 [1]  1  2  3  4  5  6  7  8  9 10

[[2]]
 [1] 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

# parse_my_vector(x = 1:10, type = "char")
# parse_my_vector(x = words[1:10], type = "num")
parse_my_vector(x = words[1:10], type = "char")

Thank you!

[[1]]
 [1] "a"        "able"     "about"    "absolute" "accept"   "account" 
 [7] "achieve"  "across"   "act"      "active"  

[[2]]
 [1] "a"   "abl" "abo" "abs" "acc" "acc" "ach" "acr" "act" "act"

# parse_my_vector(x = c(TRUE, FALSE, TRUE), type = "num")
parse_my_vector(x = c(TRUE, FALSE, TRUE), type = "logical")

Thank you!

[[1]]
[1]  TRUE FALSE  TRUE

[[2]]
[1] 2

# parse_my_vector(x = 1:10, type = "nums")