Ahmad Mousavi

Ahmad Mousavi

Assistant Prof. of Data Science,
Dept. of Math. and Stat.,
American University

Lab 2: Pipes, Functions, and Conditionals

DATA 412/612 · Week 2 · PDF · Source (.qmd)

Use a pipe, then write a function with a conditional and a check on the inputs.

Work in a Quarto document (or R Markdown if you already started one). Number the exercises. Keep only the code that answers the question.

Do 2.1 through 2.3 first. You will need a pipe, function(), if / else, and stopifnot().

1. Using a pipe

Use a pipe to:

  1. draw 100 values from a normal distribution with mean 0 and standard deviation 8
  2. take absolute values
  3. take square roots
  4. replace each value by the largest integer that is still smaller than it
  5. show the first 10 results

Do this without intermediate objects.

Useful functions: rnorm(), abs(), sqrt(), floor(), head().

2. Write add_half()

Write a function of two arguments: a numeric vector x and a numeric scalar y.

The returned vector should keep the first half of x unchanged, and add y to the second half.

If length(x) is odd, the middle value is a random choice: either the middle of x, or the middle of x + y.

Choose a clear name if you prefer another one, but the examples below use add_half(). Write a short documentation header.

Useful functions: length(), %% (even vs odd), floor(), sample(), c(), and [...]. You will need a conditional.

Example when the length is odd. The middle 3 happened to be kept; another run could have used 4:

x <- c(1, 1, 3, 1, 1)
y <- 1
add_half(x, y)
## Error in `add_half()`:
## ! could not find function "add_half"
# [1] 1 1 3 2 2

Example when the length is even:

x <- c(1, 1, 2, 2)
y <- 1
add_half(x, y)
## Error in `add_half()`:
## ! could not find function "add_half"
# [1] 1 1 3 3

Plan the steps before you type:

  1. take x and y
  2. find length(x)
  3. decide even or odd (%%)
  4. if even: take half the length; build c(first_half, second_half + y)
  5. if odd: floor() of half the length; sample() the middle from x or x + y; build c(first_half, middle, second_half + y)
  6. return the new vector

3. Check the inputs

Add stopifnot() so x is a numeric vector and y is a single numeric value. ?length, ?is.numeric, and ?is.vector are enough.

These calls should fail:

x <- c(1, 1, 1, 1)
y <- c(1, 2)
add_half(x, y)
## Error in `add_half()`:
## ! could not find function "add_half"
# Error in add_half(x, y): length(y) == 1 is not TRUE

x <- c(1, 1, 1, 1)
y <- "0"
add_half(x, y)
## Error in `add_half()`:
## ! could not find function "add_half"
# Error in add_half(x, y): is.numeric(y) is not TRUE

Show at least two failing checks in your document, including the error.