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Introduction to Lattice Graphics Richard Pugh 4 th December 2012

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Agenda Overview of Lattice Functions Creating basic graphics Panelled Graphics Grouped Data Multiple Variables Writing Panel Functions Summary

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The Data We Will Use Something relevant and sector independent London Tube Performance Data from the TFL website Excess Travel Hours by Line tube-network-performance-data

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Overview of Lattice Graphics

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One of the graphic systems of R (others include Traditional and GGPlot) An implementation of the S+ Trellis Graphics Written by Deepayan Sarkar, Fred Hutchinson Cancer Research Center

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List of Lattice Graphic Functions FunctionDescriptionGraph Type xyplot Scatter plotBivariate histogram Univariate histogramUnivariate densityplot Univariate density line plotUnivariate barchart Bar chartUnivariate bwplot Box and whisker plotBivariate qq Normal QQ plotUnivariate dotplot Label dot plotBivariate cloud 3D scatter plot3D wireframe 3D surface plot3D splom Scatter matrix plotData Frame parallel Multivariate parallel plotData Frame

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Key Function Arguments ArgumentDescription x Plot definition, typically as a formula data The data frame used for the graphic subset Any subsets to be applied to the data panel Function used to draw data in each panel groups Grouping variable for the plot Type of graphFormulaY axisX axisZ axis Univariate~ YY-- BivariateY ~ XYX- 3DZ ~ X*YYXZ Data Frame~ DataData--

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Creating Basic Graphics

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Panelled Graphics

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Specifying Panels We can use the vertical pipe symbol | in order to specify panels to be plotted This allows us to create the graphics by one or more variables

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Panel Variables During the plot creation, lattice builds a plot data frame containing the variables to plot By this time, any categorical by variables need to be factors So, either change them to characters or factors beforehand

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Panel Ordering! If you have a factor variable, the ordering of the panels is in graph and not table order (!!) We can resolve using as.table = TRUE Note that the converting of characters to factors uses alphabetical ordering

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Grouped Data

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We can specify groupings within our data in order to plot these groupings separately By default, lattice will vary styling of the groups specified The key argument is the groups argument

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Take care!

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Controlling Styles Best done via the underlying lattice style templates Use of par.settings argument which takes a list of styles We usually use a basic template and change elements of it The show.settings function lets you see the current (or adapted) styles

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Multiple Variables

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We can specify one or more X or Y axis variable in our lattice formula This can overwrite the groups input The outer argument controls how the multiple X/Y variables should be plotted

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Writing Panel Functions

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Panel Functions For each lattice graph, R performs the following actions: Partitions the data Draws the graph outline (i.e. the panels) Passes the data for each panel into the panel function We can overwrite this panel function and supply our own …

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Panel Functions The default panel function for a lattice function is panel.NameOfFunction Lets look at panel.xyplot …

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Arguments for styling Jitter & other less used bits Lets write our own panel function …….

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Now what? Now we can insert other functions into a panel function which will then impact each individual plot panel We can call: Lattice low level functions ( lpoints, ltext, llines, lpolygon etc) Existing panel. functions that exist for this purpose

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Summary

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This was just a quick overview of lattice graphics I hope it was useful For more info, look in the Lattice book, find examples online or contact Mango …

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