Functions, loops and conditional statements

ANU BDSI
workshop Introduction to R programming

Emi Tanaka

Biological Data Science Institute

3rd April 2024

Current learning objective

-Conduct elementary arithmetic operations using R
-Navigate the RStudio interactive development environment (IDE)
-Install external packages in R to extend functionality
-Comprehend various object types in R
-Manipulate lists, matrices, and vectors in R
-Compute basic summary statistics including mean, median, quartiles, and standard deviation using R
-Grasp the concept of missing values within the R environment
-Import and export data in R
Create basic functions, employ conditional statements, and utilize for loops in R
Decipher error messages and do basic troubleshooting

The content in this slide will be hard for those new to programming!

Don’t give up!

Functions

A function in R has three parts:
- formals(): the list of input arguments,
- body(): the code inside the function,
- environment(): the environment (out of scope for this workshop).
Writing your own functions can make repetitive tasks easier.
You can make a new function using function().

Examining functions

Writing the name of the function without arguments shows the internal code:

Conditional statements

The condition in the if statement needs to evaluate to a single TRUE or FALSE
ifelse() is the vectorised version of if() and else statement.

Example

Loops

Basic troubleshooting

Whether you are good at programming or not, you will inevitably encounter errors.
If you encounter an error,
1. Read the error message!
2. Google the error message or ask generative AI (like chatGPT)
3. Ask for help with a reproducible example

Reproducible Example with `reprex` LIVE DEMO

Copy your minimum reproducible example then run

reprex::reprex(venue = "slack")

Once you run the above command, your clipboard contains the formatted code and output for you to paste into places like GitHub issues, Stackoverflow and forums powered by Discourse, e.g. RStudio Community.

Asking for help

How about the question on the right?
What makes it hard or easy for people to answer this question?

Checklist (note: not an exhaustive checklist)

Is the problem clearly and succinctly described? Is the expected solution or behaviour outlined? Are you asking the right people at the right place?

If the question is asked in an public forum or similar:

Can people who can answer your question find your question? E.g. does the post have appropriate tags or keywords to reach the right experts?

If the problem is computer system related…

Can the problem be easily reproduced on other people’s system? Is the minimum reproducible code or steps supplied?

If the problem is based on data …

Is the data supplied? If the data is big, could you cull your data further to communicate or reproduce the problem?

Summary

Write new functions using function().
Use if, else, and ifelse for conditional statements.
Use for loops for repetitive tasks.
Troubleshoot errors by reading the error message and asking for help with a reproducible example.
Reproducible examples can be generated using the reprex package.

Exercise time

10:00