Analysing Social Science Data Using R

Transcription

1 Analysing Social Science Data Using R Class 8: Advanced Data Visualization m.bojanowski@icm.edu.pl April 4, 03 GSSR, Warsaw

2 Outline Plotting systems Function matplot 3 Building a chart step by step 4 Colors 5 Examples

3 Outline Plotting systems Function matplot 3 Building a chart step by step 4 Colors 5 Examples

4 Plotting systems in R Definition (Plotting system) A collection of functions for creating charts. There are several plotting systems in R, mainly: base The oldest and the simplest (yet powerful). Contained in the base installation of R. Functions in preinstalled package graphics. lattice Focused on multivariate visualizations. Package lattice. ggplot Newest of the three. Very extensive. Rich collection of graphical elements. Relatively harder to customize. Package ggplot. We will explore the base system

5 Outline Plotting systems Function matplot 3 Building a chart step by step 4 Colors 5 Examples

6 Function matplot Plotting several data series (multiple series of lines/points) on the same plot. matplot(x, y, type="p",...) Plotting columns of x against columns of y. Accepts familiar arguments like pch, lty, lwd, col etc.

7 Small matplot example data mx <- matrix(:8, ncol=) my <- matrix(c(,,3,4,5,3,,), ncol=) mx ## [,] [,] ## [,] 5 ## [,] 6 ## [3,] 3 7 ## [4,] 4 8 my ## [,] [,] ## [,] 5 ## [,] 3 ## [3,] 3 ## [4,] 4

8 Plotting a matrix against common x s matplot(mx[,], my) my mx[, ]

9 Plotting a matrix against common y s matplot(mx, my[,], type="l") my[, ] mx

10 Plotting two matrices matplot(mx, my, type="b", col="black") my mx

11 More extensive matplot example () Salaries by age and gender in PGSS 008: pgss$kobieta <- pgss$q8 == s <- subset(pgss, pgssyear=008) ageg <- with(s, cut(q9age, c(-inf, seq(5, 70, by=5), Inf))) salary <- with(s, replace(q3, which(q3 %in% c(-, -9, 0)), NA)) m <- with(s, tapply(salary, list(ageg, kobieta), mean, na.rm=true)) head(m) ## FALSE TRUE ## (-Inf,5] ## (5,30] ## (30,35] ## (35,40] ## (40,45] ## (45,50]

12 More extensive matplot example () matplot(m, type="b") m

13 Outline Plotting systems Function matplot 3 Building a chart step by step 4 Colors 5 Examples

14 Essential steps When creating charts the steps to perform include: Set up the coordinate system Add data-related elements (points, lines, polygons, etc.) 3 Add data annotations (axes, legends, additional text) 4 Add titles

15 Overview of low-level plotting functions Some functions: data-related elements points, lines, polygon, rect, arrows, abline, text annotation axis, legend titles title, mtext

16 Setting up the chart To setup the coordinate system you can e.g.: Call plot with type="n", and possibly setting xlim and ylim explicitely. Call matplot with type="n" Most plotting functions have an argument like type with which you can suppress the actual plotting. Setting arguments ann (annotations) and axes to FALSE will suppress default axis and titles.

17 Graphical parameters There are many additional arguments that you can specify to modify a plot. See?par. op <- par(mar=c(,,,)) # set new margins and save old in 'op' # Here you do the plotting plot(:5) # etc. par(op) # reset to previous values of 'par'

18 Points and lines Add a series of points and/or join them with lines points(x, y,...) lines(x, y,...) where x and y are vectors of point coordinates. Accepts familiar arguments like pch, lty, lwd, col etc.

19 Adding text Add texts at x,y coordinates. This works almost like points text(x, y, labels,...) Additional arguments pos Position of text relative to (x,y) point. font Font variant to use: =normal, =bold, 3=italics, 4=bold italics

20 Axes Add an axis to the plot axis( side, at, labels,...) side One of =bottom, =left, 3=top, 4=right at Vector of tick positions labels Vector of labels For example: axis(3, at=:4, labels=c("a", "b", "c", "d"))

21 Legend Add a legend legend(x, y=null, legend, pch, lty, lwd,... ) x, y Position of upper-left corner of the legend. x can be a textual description like "lowerright", "up" etc. legend Character vector of legend labels. pch,lty Symbols to be plotted next to labels. For example: legend("lowerleft", legend=c("men", "Women"), lwd=, col="black", lty=:)

22 Titles Adding plot titles and axis titles. title( main, sub, xlab, ylab ) mtext( text, side, line ) title Adds main title, subtitle or titles for X or Y axes mtext Adds a text to a plot margin, like xlab or ylab, but to any of the four sides.

23 Outline Plotting systems Function matplot 3 Building a chart step by step 4 Colors 5 Examples

24 Ways to specify colors Specifying colors numbers Use colors from the set palette, see?palette color names Use one of 657 built-in color names hex codes Color symbol like #ffffff (white) or # (black), or #0a7bc etc..

25 Color palettes You can select colors more systematically using color palettes and color ramps. rainbow(5) ## [] "#FF0000FF" "#CCFF00FF" "#00FF66FF" "#0066FFFF" ## [5] "#CC00FFFF" # install.packages("rcolorbrewer") library(rcolorbrewer) brewer.pal(5, "Set") ## [] "#E4AC" "#377EB8" "#4DAF4A" "#984EA3" "#FF7F00" See the color reference sheet

26 Outline Plotting systems Function matplot 3 Building a chart step by step 4 Colors 5 Examples

27 Plotting summaries of several variables in6j in6i in6h in6g in6f in6e in6d in6c in6b in6a Fair salary [PLN]

28 Summaries, version in6j in6i in6h in6g in6f in6e in6d in6c in6b in6a Fair salary [PLN]

29 Chartjunk from GUS