CS代写|R语言代写R language代考|STA518

CS代写|R语言代写R language代考|Aims of this chapter

Three main data plotting systems are available to R users: base R, package ‘lattice’ (Sarkar 2008) and package ‘ggplot2’ (Wickham and Sievert 2016), the last one being the most recent and currently most popular system available in $\mathrm{R}$ for plotting data. Even two different sets of graphics primitives (i.e., those used to produce the simplest graphical elements such as lines and symbols) are available in $R$, those in base $R$ and a newer one in the ‘grid’ package (Murrell 2011).

In this chapter you will learn the concepts of the grammar of graphics, on which package ‘ggplot2’ is based. You will also learn how to build several types of data plots with package ‘ggplot2’. As a consequence of the popularity and flexibility of ‘ggplot2’, many contributed packages extending its functionality have been developed and deposited in public repositories. However, I will focus mainly on package ‘ggplot2’ only briefly describing a few of these extensions.

To run the examples included in this chapter, you need first to load some packages from the library (see section $5.2$ on page 163 for details on the use of packages).

CS代写|R语言代写R language代考|Introduction to the grammar of graphics

What separates ‘ggplot2’ from base $R$ and trellis/lattice plotting functions is the use of a grammar of graphics (the reason behind ‘gg’ in the name of package ‘ggplot2’). What is meant by grammar in this case is that plots are assembled piece by piece using different “nouns” and “verbs” (Cleveland 1985). Instead of using a single function with many arguments, plots are assembled by combining different elements with operators $+$ and $\%+\%$. Furthermore, the construction is mostly semantics-based and to a large extent, how plots look when printed, displayed, or exported to a bitmap or vector-graphics file is controlled by themes.

We can think of plotting as representing the observations or data in a graphical language. We use the properties of graphical objects to represent different aspects of our data. An observation can consist of multiple recorded values. Say an observation of air temperature may be defined by a position in 3-dimensional space and a point in time, in addition to the temperature itself. An observation for the size and shape of a plant can consist of height, stem diameter, number of leaves, size of individual leaves, length of roots, fresh mass, dry mass, etc. If we are interested in the relationship between height and stem diameter, we may want to use cartesian coordinates, mapping stem diameter to the $x$ dimension of the plot and the height to the $y$ dimension. The

The grammar of graphics allows us to design plots by combining various elements in ways that are nearly orthogonal. In other words, the majority of the possible combinations of “words” yield valid plots as long as we assemble them respecting the rules of the grammar. This flexibility makes ‘ggplot2’ extremely powerful as we can build plots and even types of plots which were not even considered while designing the ‘ggplot2’ package.

When a plot is built, the whole plot and its components are created as R objects that can be saved in the workspace or written to a file as objects. The graphical representation is generated when the object is printed, explicitly or automatically. The same ggplot object can be rendered into different bitmap and vector graphic formats for display or printing.

Even if we do not explicitly add them all, default elements may be used. The production of a rendered graphic with package ‘ggplot2’ can be represented as a flow of information: data $\rightarrow$ scale $\rightarrow$ statistic $\rightarrow$ aesthetic $\rightarrow$ geometry $\rightarrow$ coordinate $\rightarrow$ ggplot $\rightarrow$ theme $\rightarrow$ rendered graphic.

R语言代考

CS代写|R语言代写R language代考|Aims of this chapter

R 用户可以使用三个主要的数据绘图系统：base R、“lattice”包（Sarkar 2008）和“ggplot2”包（Wickham 和 Sievert 2016），最后一个是最新和当前最流行的系统R用于绘制数据。在R, 那些在基地R以及“网格”包中的一个较新的包（Murrell 2011）。

CS代写|R语言代写R language代考|Introduction to the grammar of graphics

‘ggplot2’ 与基础的区别是什么R和格子/格子绘图功能是使用图形语法（包’ggplot2’名称中’gg’背后的原因）。在这种情况下，语法的意思是情节是使用不同的“名词”和“动词”逐段组装的（Cleveland 1985）。不是使用具有多个参数的单个函数，而是通过将不同元素与运算符组合来组装图+和%+%. 此外，构造主要是基于语义的，并且在很大程度上，打印、显示或导出到位图或矢量图形文件时绘图的外观由主题控制。

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