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--- notes:r_cheat_sheet [2026/11/03 02:36]
47.79.200.19 old revision restored (2026/09/04 02:04)
+++ notes:r_cheat_sheet [2026/11/03 05:09] (current)
157.100.198.61 old revision restored (2026/08/03 07:09)
@@ Line 3: / Line 3: @@
 [[http://www.r-project.org/ | R]] is a free software environment for statistical computing and graphics. These notes summarize the [[http://tryr.codeschool.com/ | free R CodeSchool tutorial]].
+===== Basics =====
+  * ''R'' is the command-line interpreter
+  * Expressions are evaluated and displayed e.g. 1, 1+1, "Hello World"
+  * Booleans are e.g. ''1=1'' , ''3>4'' , ''TRUE'', T, ''FALSE'', F
+  * For variable assignment ''x=1'' or ''x<-1''
+  * For help on a function use ''help(sum)'' or ''example(sqrt)''
+  * Operations are ''+ - * / = <-''
+  * ''NA'' is used to express a missing or unknown data  value. Expressions on NA return NA.
+===== Vectors =====
+  * To create a vector, use the combine command ''c(4,7,9)''
+  * Vectors must be of the same type, and are cast if not (e.g. to strings).
+  * ''a:b'' creates a vector of integers from a to b.
+  * ''seq(a,b,s)'' creates a vector of numbers from a to b in increments of s
+  * ''myseq[3]'' to access third element i.e. vectors indexed starting at 1.
+  * Use a vector as an index to access multiple elements e.g. ''myseq[c(1,3)]''
+  * The ''names'' function can be used to assign names to vector elements. Once names are asigned, they can be used as indices e.g. <code>
+names(myseq)=c('one','two','three')
+myseq['two']</code>
+  * ''myseq + 1'' adds one to all elements of the myseq vector.
+  * Scalar operations or functions on vectors typically produce other vectors e.g. + - == sin(myseq)
+===== Plotting =====
+  * ''barplot[myseq]'' creates a bar plot of the ''myseq'' vector. ''abline(h=y)'' plots a horizontal line at height y.
+  * ''plot[x,y]'' plots x vs y e.g. <code>
+x=seq[0,20,.1]
+y=sin(x)
+plot(x,y) </code>
+  * ''contour(mymat)'' plots a contour map of a matrix.
+  * ''persp(mymat)'' plots a contour map in perspective.
+  * ''image(volcano)'' generates a heat map of the matrix.
+===== Matrices =====
+  * ''matrix(0,3,4)'' creates a 3x4 matrix with all elements 0.
+  * ''matrix(1:12,3,4)'' creates a 3x4 matrix with numbers 1-12.
+  * dim(myseq) can be used to change dimensions of a matrix
+  * ''mymatrix[3,4]'' returns an element of the matrix (row,column).
+  * ''mymatrix[,2]'' returns entire second column.
+===== Statistics =====
+  * ''mean(myvec)'' returns the mean.
+===== File Handling =====
+  * ''list.files()'' to list files in furrent directory
+  * ''source("file.R")'' to load file of code

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