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--- notes:r_cheat_sheet [2026/09/15 05:07]
88.188.251.74 old revision restored (2026/07/20 13:31)
+++ notes:r_cheat_sheet [2026/09/15 06:37] (current)
47.238.237.38 old revision restored (2026/08/09 14:13)
@@ Line 6: / Line 6: @@
   * ''R'' is the command-line interpreter
+  * ''install.packages("ggplot2") '' to install additional packages
   * 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)''
+  * For help on a function use ''help(sum)'' ,  ''help(package='ggplot2')''  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)''
@@ Line 36: / Line 37: @@
   * ''persp(mymat)'' plots a contour map in perspective.
   * ''image(volcano)'' generates a heat map of the matrix.
+  * ''qplot(weights, prices, color=types)'' - more attractive plotting using ggplot2 package.
 ===== Matrices =====
@@ Line 44: / Line 45: @@
   * ''mymatrix[3,4]'' returns an element of the matrix (row,column).
   * ''mymatrix[,2]'' returns entire second column.
+===== Data Sets =====
+  * ''factor'' is a collection type for categorized values - ''myfac=factor(myvec)''
+  * ''factor''s group unique string values as ''level''s e.g. levels(myfac) shows unique levels.
+  * ''as.integer(myfac)'' shows levels as integers, can be used to set plot type
+  * ''legend("topright", levels(types), pch=1:length(levels(types)))''
+  * A data frame collects sets of related values (i.e. sets of columns with values in the same order) e.g. ''mydf=data.frame(weights,prices,types)''
+  * To extract a column, use double-square brackets with the column index or name e.g. ''mydf%%[['weights']]%%'' or just a dollar sign e.g. ''treasure$prices''
+  * ''merge'' merges data sets by joining on shared column names
 ===== Statistics =====
-  * ''mean(myvec)'' returns the mean.
+  * ''mean(myvec)  median(myvec)   sd(myvec)''
+  * ''cor.test'' tests for correlation (Pearson's product-moment)
+  * ''line = lm(cola ~ colb)'' calculates a linear model between cola and colb that can be plotted with ''abline(line)''
+  *
 ===== File Handling =====
   * ''list.files()'' to list files in furrent directory
   * ''source("file.R")'' to load file of code
+  * ''read.csv('mydat.csv')'' to load a csv file
+  * ''read.table'' to read text data with other separators
+  * ''con<-url("http://google.com","r")'' to read a webpage
+  * ''x<=readLines(con)'' to convert to an array of lines

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