In homerhanumat/bcscr: Beginning Computer Science with R

Caveat: This document provides a convenient, worry-free format for writing an article for R Pubs. Of course you must modify it properly. In particular you must delete any instructional material (such as this paragraph, for instance), and don't keep the example shown in this document. Also, do not forget to provide your own name and title in the YAML front matter.

# You should also load any packages that you need, for example:
# library(ggplot2)

# This is a good place for global chunk options;
# we'll get you started with a few sensible ones.
# Don't try to modify them until you have more experience.
knitr::opts_chunk$set(
  error = TRUE,         # document will knit even if code-chunk contains error
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                        # document
  size = "small",       # slightly smaller LaTeX output
  tidy = FALSE          # show code like you wrote it
 )

The Problem: Reversing a Vector

Our problem is to write a function called reverse() that when given a vector returns a vector whose elements are the results of the given vector. The function is supposed to take a single parameter called vec, the vector to be reversed, and the default value of vec is supposed to be c("Bob", "Marley").

A Hint

This problem is difficult enough that we might not be able to write down the function from scratch, so we should take our time and build up to it in a sequence of small steps.

Step One: Reverse a Specific Vector

In order to reverse the following vector of length five:

firstFiveLetters <- c("a", "b", "c", "d", "e")

we simply subset the vector in reverse order:

firstFiveLetters[5:1]

Step Two: Generalize

In the above code we can get the 5 as length(firstFiveLetters), the following code would have worked just as well:

firstFiveLetters[length(firstFiveLetters):1]

Let's try this out on some other vector called vec:

vec <- c("Raj", "Bettina", "Salome")  # here you can set the vector
vec[length(vec):1]                    # this line does the work of reversing

Step Three: Encapsulate Into a Function

Now we are ready to encapsulate the working code into a function. The default value should be provided when we state the parameter:

reverse <- function(vec = c("Bob", "Marley")) {
  # the working code goes here!
}

You need to replace the comment above with the code that will reverse vec.

Step Four: Test Your Function

Don't forget to write some code to test your function. You should test it with no input to see that the default-values really work, and also with vec set to another vector that overrides the default.

homerhanumat/bcscr documentation built on Jan. 14, 2023, 4 a.m.