R Programming for Music
Donald Byrd
rev. 21 March 2008
Copyright © 2006-08, Donald Byrd
Intrroducing R
• R is very interactive: instead of programming, can use as
powerful graphing calculator
• => easier to experiment with & learn, & useful that way
• R was originally designed for statistics
• Why R?
– easy to do simple things with it
– easy to do many fairly complex things, incl. graphs &
handling audio files
• probably not good for really complex programs
– free, & available for all popular operating systems
– very interactive => easy to experiment
– has good documentation
– In use in other Music Informatics classes, & standardizing is
30 Jan. 08
Getting started with R
• To get R
– Web site: http://cran.us.r-project.org/
– Has lots of documentation (tutorials, manuals, etc.), too…
though most isn’t for beginners
– Versions for Linux, Mac OS X, Windows
– On all(?) STC computers
• Tutorial:
• http://www.informatics.indiana.edu/donbyrd/Teach/RTools+Do
• Can use R interactively as a powerful graphing, musicing, etc.
• …but it’s not perfect: sometimes very cryptic
30 Jan. 08
Programming in General (1)
• Details are often vital (& errors are costly)
– A great many details really are. Commonly:
• Quote marks, including single vs. double
• Capitalization
– “Wav” & “wav” are different
– TIP: “steal” as much as possible!
• Via Copy & Paste is ideal: avoids typos
• Programs tend to be very hard to understand
– TIP: include useful, readable comments
– TIP: choose variable names for clarity
• “wavdata” isn’t good; how about “samples”?
– TIP: consistency helps clarity and correctness
• Don’t mix “v = expr”, “v <- expr”, and “expr -> v”
• Use the same variable name for something in every prog.
• Program defensively
27 Nov. 07
Programming in General (2)
• Comments
– Classic example of a bad comment
• x <- x+1
# add 1 to x
– Doesn’t explain anything!
• Good commenting style (thanks to Ed Wolf)
# Using the Add Sines Demo, create and play a wave at G3,
# then do the same for a wave at 5/4 this frequency. Finally,
# normalize the sum of the two waves and listen to result.
# create and play first sound wave
sndW <- sine(f, duration=secs, samp.rate=sr, bit=16, xunit="time")
play(sndW )
rev. 3 Apr. 07
Programming in General (3)
• Block comments (w/ overall description) more
important than comments on single stmts
• Ideal: say just the right things: not too much or
too little
– Basic principle of all human communication
– …including this slide show & music notations (CMN,
tablature, etc.)
– …and comments in a program
• Other aspects of formatting & style
– Variable names
• Choose variable names for clarity
• camelCase is helpful
– Space around operators
– “v <- f(expr)”, not “v<-f(expr)”
3 April 2007
Programming in R (1)
• R offers to save workspace when you quit
– Are you sure it’s what you want?
– TIP: Just say no.
• Can restore original with ‘load(".Rdata")’ or menu command
– TIP: Use a text editor & files to save work
• If real text editor (not word processor) file, can run with R
“source” command
• Regardless, can Copy & Paste, even just part of file
• setwd() to correct path for your computer
– Depends on where you have files
– Can be tricky, esp. in Windows
• Typical Windows ex.: setwd("C:/Documents and
• On Mac (& Windows?), can use “~/Teaching/N560"
• …or drag & drop
• …or use R GUI “Change Working Directory” menu command!
rev. 30 Jan. 08
Programming in R (2)
• R has many useful built-in functions
– Many of them handle vectors (no loop needed)
• diff(v): vector of consecutive differences
• sum(v): sum of vector elements
– Random numbers with various distributions: runif
(uniform), rnorm (normal), etc.
– read.table, table (and related functions)
– fft
– tuneR adds sine, square, noise, bind, mono, etc.
• R (and tuneR) have excellent on-line help
– Type either ‘help(sine)’ (e.g.) or ‘?sine’
• …but NB: sometimes need ‘help("sine")’
– TIP: Copy & Paste from help window!
– Caveat: terminology is statistics oriented
rev. 14 Jan. 08
Programming in R (3)
• Besides built-in, functions can be user-written
– Hard for many beginners; why?
– Probably mostly confusion about variables (including
parameters & return values)
• A simple but realistic example
# Convert MIDI note number to frequency in Hertz.
MIDINum2Freq <- function(noteNum) {
freq <- 440*2^((noteNum-69)/12)
• Calling it
– fr <- MIDINum2Freq(57)
# Sets fr = 220
– Inside function, parameter noteNum = 57, freq = 220; fr
doesn’t exist (it’s out of scope)
– Outside function, noteNum & freq don’t exist
rev. 30 Jan. 08
Programming in R (4)
• Introducing loops
– Loops also hard for many beginners
– Main reason is probably confusion re control variable
– A very simple (though pointless) example
mnnV <- 1:6
# make mnV a 6-place vector
# see what mnnV is before loop
for (n in 1:6) {
mnnV[n] <- n+59
# ...and after
– Instead of “in 1:6”, can use any vector!
– n (control variable) doesn’t exist outside the loop
– C, Perl, etc. users can put the vector in the “for”
• for (n in seq(1, 6)) { …
– Loop is a type of control statement
rev. 30 Jan. 08
Software Engineering & Debugging (1)
• Experience: all complex programs have bugs
– Judge in Florida e-voting case: claim that voting
machine software was buggy is speculation
– True, but… !
• Disclaimer: I don’t know any hard evidence
• Expect bugs & program defensively
• True stories
– The program that failed only on Wednesdays! Why?
• Hint: “Wednesday” has 9 characters
– Weeks of debugging to find a “1” that should have
been “i”
27 Nov. 07
Software Engineering & Debugging (2)
• Good engineering (design, coding, comments,
etc.) => less debugging & more robust (reliable &
flexible) programs
• Don’t underengineer
• …but don’t overengineer, either!
• Underengineering is much bigger danger for
inexperienced programmers
• Main factors
– Complexity of problem
– Is program or code it includes likely to be used for very
• If so, how expert are future programmers likely to
27 Nov. 07
Software Engineering & Debugging (3)
• Standard technique: zero in on problem code
• Debug on short/simple cases, not long/complex
– Makes it practical to look at results of several print
– Reduces or eliminates long delays to see results
– “short/simple” often means simply not much data
– Can easily reduce days of debugging to hours
• Usually easy to do by turning lots of data into a
little data
Real situation: nThemes <- 3500, or 20 sec. audio file
For testing: use nThemes <- 4 (say), or 1 sec. audio
Caveat! the “little” data may not show the bug
…and if bug results from a design problem, fixing it
may be very hard
27 Nov. 07
Debugging in R (1)
• Basic technique: zero in on bug with print or cat
– E.g., before & after doing something questionable
• print(c("max before scaling=", max([email protected])))
• wNotes <- wNotes*2.5
• cat("max after scaling=", max([email protected]), “\n”)
– cat merges its arguments, gets rid of the extra parens
– …but doesn’t end the line => do it yourself with “\n”
– If you use “source” (& inside loops?), just naming
variable doesn’t work; must use print or cat
• A variation: use plot instead of print/cat
– The right picture is worth 10,000 words; the wrong
one, zero (cf. Tufte on the Challenger disaster)
– …but the right picture for debugging is often simple &
31 Jan. 08
Debugging in R (2)
• More advanced technique: use a good debugger
– Allows setting breakpoints, looking at variables, etc.,
while program is running
– Especially helpful w/ complex programs
– …or learning a new language
– To some extent, R’s interactivity accomplishes same
• R has a debugger
– One student (an experienced programmer) tried &
liked it! Anyone else?
8 Sept. 07
Dangers of R (1)
• More danger of nasty bugs in R than many programming
languages & environments
– No explicit types => can’t warn of questionable usage
– No variable declarations => catches fewer typos (only a
problem in old versions of R?)
– Both above like Perl (e.g.), but Java (e.g.) is great on both =>
Java programmers likely to be careless!
• Defensive programming
– E.g., add “sanity checks” as you work, use conventions for
variable names, etc.
– Always important: a subtle bug can waste a huge amount of
time and/or money
• Ex: weeks of debugging to find a “1” that should have been “i”
• Ex: period instead of comma => missile had to be destroyed
– …but especially in dangerous environments like R
1 Feb. 08
Dangers of R (2)
• “Gotchas” in R (all from real life)
– Surprising operator precedence, esp. in “for” statement
• In sets, need parentheses to get addition before “:”
• E.g., say “start:(start+5)”, not “start:start+5” !
– “;” is usually ignored, but not always
– Line break sometimes starts a new statement, but not
• cf. “LineBreaksInRStatements.r” example
– Referring to a column of a table different ways gives
same data but can behave very differently
• “noteTbl$Cum.time” & “noteTbl[,1]” are vectors of
integers; “noteTbl[1]” is a list
rev. 23 Feb. 08
Dangers of R & tuneR
• Other real-life examples from Don’s classes
– Undeclared variable: “allNotes” vs. “allnotes” (only a problem
in old versions of R?)
– Call a function that returns a value but ignore the value
• Danger much worse because R & tuneR often gives lousy
feedback for errors or likely errors
– tuneR square & sawtooth functions fail w/o error message if
frequency isn’t an integer—and the manual doesn’t say it has
to be an integer!
– Exception: tuneR play w/ unnormalized values => very
helpful error message
– Nonexistent named params. sometimes give error, not always
rev. 24 Feb. 08
Programming in R with tuneR
• On OS X (and LINUX): play() problem
– Must say what program to use to play Waves
• Either setWavPlayer once, or add 2nd param. to
each play()
– OS X can use QuickTime Player
• It’s on every OS X machine, & it works, but…
– Usually gives scary error messages; must hit the
escape key to get R to continue; leaves open more &
more QuickTime Players. A serious nusiance.
– OS X alternative: playRWave
• Works fine, but…
– Not pre-installed; you must get & install it
• Available (with instructions) at:
– http://www.informatics.indiana.edu/donbyrd/Teach/
rev. 30 Jan. 08
Don’s Coding Conventions (1)
Chris Raphael’s & Don Byrd’s styles are very different
Variable names
Partly a matter of taste, partly reflects goals
Consistency & readability are important
Consistency helps clarity and correctness
But flexibility is important too; these are guidelines only!
General: long enuf to be clear, but no longer
Ex.: use “nNotes”, not “noteCount” or just “notes”
“Hungarian notation”: suffix “V” = vector, “W” = wave
Common examples: nNotes, sampleV, noteW, sr
Always use “<-” for assignment
Reason: with “=” for named parameters and “==” for tests,
using “=” for assignment is too confusing
rev. 20 Mar. 08
Don’s Coding Conventions (2)
Use of whitespace
Program organization
Put space before & after assignment operators
Separate parens & curly braces from adjacent things with
Put several spaces before, at least one after “#”
Initial stuff (libraries, etc.), setting “parameters” likely to change
Definitions of functions
Main program (calls the functions, if there are any)
Specific to audio: creating simple waveforms
When possible, use tuneR sine function
Create samples directly only when tuneR sine isn’t flexible
enough (for glissandi, vibrato, other waveforms, etc.)
rev. 4 Feb. 08