From Octave to R

From Octave to R

GNU-Octave is a program not unlike Matlab.

Help

Octave	R
`help -i`	`help.start()`
`help`	`help(help)`
`help sort`	`help(sort)`
	`demo()`
(Matlab) `lookfor plot`	`apropos(‘plot’)` or `help.search(‘plot’)`

Assignment

There are multiple assignment operators in R.

Octave	R
`a=1;`	`a <- 1`
`a=1`	`a <- 1; a` or `(a <- 1)`

Complex Numbers

Octave	R	Comments
`3+4i`	`3+4i`
`i`	`1i`	R treats “i” as a variable name
`abs(3+4i)`	`Mod(3+4i)`	but put a numeral in front
`arg(3+4i)`	`Arg(3+4i)`
`conj(3+4i)`	`Conj(3+4i)`	get these from help(Mod)
`real(3+4i)`	`Re(3+4i)`
`imag(3+4i)`	`Im(3+4i)`
`sqrt(-2)`	`sqrt(-2+0i)`	R has explicit complex arithmetic

Vectors

Vectors and Sequences

Octave	R
`1:10`	`1:10` or `seq(10)`
`1:3:10`	`seq(1,10,by=3)`
`10:-1:1`	`10:1`
`10:-3:1`	`seq(from=10,to=1,by= -3)`
`linspace(1,10,7)`	`seq(1,10,length=7)`
`(1:10)+i`	`1:10+1i`
`a(1:end)`	`a[1:length(a)]`

Vectors and Concatenation

Octave	R	comments
`a=[2 3 4 5];`	`a <- c(2,3,4,5)`	R output not echoed to the screen if assigned
`a=[2 3 4 5]`	`(a <- c(2,3,4,5))`	(but round brackets around an expression force echo)
`adash=[2 3 4 5]’ ;`	`adash <- t(c(2,3,4,5))`
`[a a]`	`c(a,a)`
`[a a*3]`	`c(a,a*3)`
`a.*a`	`a*a`
`a.^3`	`a^3`
`[1:4 a]`	`c(1:4,a)`

Repeating Vectors

Octave	R
`[1:4 1:4]`	`rep(1:4,2)`
`repmat(1:4,1,3)`	`rep(1:4,3)`
`repmat(1:4,3,1)`	`kronecker(matrix(1,3,1),t(1:4))`
`nonzeros(triu(repmat(1:4,4,1)))’`	`rep(1:4,1:4)`
`repmat(1:4,3,1)(:)’`	`rep(1:4,each=3)`

Negative indexing

In R, the negative indexing means that the elements are not wanted.

Octave	R
`a=1:100;`	`a <- 1:100`
`a(2:100)`	`a[-1]`	omit the first element.
`a([1:9 11:100])`	`a[-10]`	omit the tenth element.
`a([1:9 12:100])`	`a[-(10:11)]`	need parentheses: “:” operator has low priority
`a([find(mod(0:49,3)), 51:end])`	`a[-seq(1,50,3)]`	omit 1,4,7,...

Destructive modification:

Octave	R
`a(1) = []`	`a=a[-1]`	remove the first element.
`a(10) = []`	`a=a[-10]`	remove the tenth element.
`a(1:3:50) = []`	`a=a[-seq(1,50,3)]`	remove 1,4,7,...

Boolean indexing

Octave	R
`(1:3)[true false true]`	`(1:3)[c(TRUE,FALSE,TRUE)]`
`a(a>90)= -44;`	`a[a>90] <- -44`
`find(a>90)`	`which(a>90)`

Max and Min

Octave	R
`a=randn(1,4);`	`a <- rnorm(4)`
`b=randn(1,4);`	`b <- rnorm(4)`
`max(a,b)`	`pmax(a,b)` mnemonic: pairwise max.
`max([a’ b’])`	`cbind(max(a),max(b))`
`max([a b])`	`max(a,b)`
`[m i] = max(a)`	`m <- max(a) ; i <- which.max(a)`

Ranks

Octave	R
`ranks(rnorm(8,1))`	`rank(rnorm(8))`
`ranks(rnorm(randn(5,6)))`	`apply(matrix(rnorm(30),6),2,rank)`

Matrices

Binding

Octave	R
`[1:4 ; 1:4]`	`rbind(1:4,1:4)`
`[1:4 ; 1:4]’`	`cbind(1:4,1:4)` or `t(rbind(1:4,1:4))`
`[2 3 4 5]`	`c(2,3,4,5)`
`[2 3;4 5]`	`rbind(c(2,3),c(4,5))` rbind() binds rows
`[2 3;4 5]’`	`cbind(c(2,3),c(4,5))` or `matrix(2:5,2,2)`
`a=[5 6];`	`a <- c(5,6)`
`b=[a a;a a];`	`b <- rbind(c(a,a),c(a,a))` see repmat below
`[1:3 1:3 1:3 ; 1:9]`	`rbind(1:3, 1:9)`
`[1:3 1:3 1:3 ; 1:9]’`	`cbind(1:3, 1:9)`
`[repmat(1:3,1,8)(1:8);1:8]`	`rbind(1:3, 1:8)`

Other

Matlab	R	Comments
`tic`	`tic= function() {.first.time «- proc.time()}`
`toc`	`toc= function() {proc.time()- .first.time}`	then use `tic(); command; toc();` as usual

Debugging

Matlab	R	Comments
keyboard	browser() ; debug(“function_name”)	to exit debugging mode see below
return	Q	Halt execution and drop to top level see Here, chapter 9 (Debugging)
ans	.Last.value
disp(44)	print(44)

Plotting

Matlab	R	Comments
a=rand(10)	a <- array(runif(100),c(10,10)) or matrix(runif(100),nrow=10)
help plot	help (plot) and methods(plot)
plot(a)	matplot(a,type=”l”,lty=1)
plot(a,’r’)	matplot(a,type=”l”,lty=1,col=”red”)
plot(a,’x’)	matplot(a,pch=4)	see example(“points”) for the symbols
plot(a,’–‘)	matplot(a,type=”l”,lty=2)
plot(a,’x-’)	matplot(a,pch=4,type=”b”,lty=1)
plot(a,’x–‘)	matplot(a,pch=4,type=”b”,lty=2)
semilogy(a)	matplot(a,type=”l”,lty=1,log=”y”)
semilogx(a)	matplot(a,type=”l”,lty=1,log=”x”)
loglog(a)	matplot(a,type=”l”,lty=1,log=”xy”)
plot(1:10,’r’), hold on, plot(10:-1:1,’b’)	plot(1:10,col=”red”,type=”l”); matplot(10:1,col=”blue”,type=”l”,add=TRUE) or matlines(10:1,col=”blue”)
plot([1:10 10:-1:1]), axis equal	? not sure ? maybe MASS::eqscplot(1:10,10:1)

to be continued

Based on a reference sheet translating between the most common Octave (or Matlab) and R commands provided by Robin Hankin.

Also see Dave Hiebeler’s extensive reference guide

— Romain François 2006/03/04

— Kath 2009/06/10