R EssentialsChristopher Manning4 November 2007Here are some collected pointers on some useful things that you should have picked up, but just to makesure that you have. . . .1 Data manipulation1.1 Creating vectors• c(11, 19, 23, 7) Creates a vector of the given items• seq(1, 10) or 1:10 or seq(1, 10, 0.1) creates vectors that are sequences incrementing by 1 or theamount given• rep(c(3,6,9), 3) and especially rep(1:2, c(12, 19)) replicates a list k times, or each item in alist the number of times shown – useful for making things like group codes for later selection.• matrix(c(4, 8, 11, 2, 9, 7), nrow=3, byrow=T) is one way to make a matrix.• rbind(c(4,8), c(11,2),c(9,7)) or cbind(c(4, 11, 9), c(8, 2, 7)) make the sa me matrix bygluing rows or columns to gether.1.2 Manipulating data framesWhile you can get out and manipulate parts of a data frame using array indexing and conditional expressions,usually there are e asier to use functions.• spdative <- subset(dative, dative$modality=="spoken") The subset() function gives you a sub-set of a da ta frame. The first argument is the data set, the se c ond aargument is an expression to selectrows, and a n optional third argument will select columns.• spdative <- transform(spdative, ThemeMinusRecipient = LengthOfTheme - LengthOfRecipient)The transform() function lets you add columns to a data frame. (Think of it that you are adding columnswith variable transformations, as here.) You can e ither save the result in the same data frame objector in a new object.2 Plots2.1 Saving plots• You make a pdf plot like this (the filename is up to you; this is for Unix):pdf("~/ling289/example.pdf")plot(x, y) dev.off()It’s a slightly awkward recipe, but it’s what you do. You can do the same with many other file types.Other good ones to know are postscript(), xfig(), and jpe g().12.2 Adding stuff to plots• lines(c(150000, 200000, 250000), c(59.5,60,61)) Add lines to a plot joining the points specifiedby two vectors• abline(h=60.25), abline(v=200000), abline(a=59.75, b=0.1), and abline(lm(mt03.ter ~ train.vocab))Add lines to a plot horizontally, vertically, with intercept and slope, and according to the b e st fit of alinear