R语言实战（三） 图形初阶

3.1 使用图形

• plot：基础绘图
• abline：添加回归直线
• hist：绘制直方图
• boxplot：绘制箱线图

• dev.new()：returns the return value of the device opened, usually invisible NULL.
• dev.cur(): returns a length-one named integer vector giving the number and name of the active device, or 1, the null device, if none is active.
• dev.list(): returns the numbers of all open devices, except device 1, the null device. This is a numeric vector with a names attribute giving the device names, or NULL is there is no open device.
• dev.next(which = dev.cur())：return the number and name of the next device in the list of devices. This will be the null device if and only if there are no open devices.
• dev.prev(which = dev.cur()): return the number and name of the previous device in the list of devices. This will be the null device if and only if there are no open devices.
• dev.off(which = dev.cur()): returns the number and name of the new active device (after the specified device has been shut down).
• dev.set(which = dev.next()): returns the number and name of the new active device.
• graphics.off()

Only one device is the ‘active’ device: this is the device in which all graphics operations occur. There is a "null device" which is always open but is really a placeholder: any attempt to use it will open a new device specified by getOption("device").

Devices are associated with a name (e.g., "X11" or "postscript") and a number in the range 1 to 63; the "null device" is always device 1. Once a device has been opened the null device is not considered as a possible active device. There is a list of open devices, and this is considered as a circular list not including the null device. dev.next and dev.prev select the next open device in the appropriate direction, unless no device is open.

3.2 一个简单的例子

dose <- c(20, 30, 40, 45, 60) 
drugA <- c(16, 20, 27, 40, 60) 
drugB <- c(15, 18, 25, 31, 40)
plot(dose, drugA, type="b")

3.3 图形参数

• plot(x, y, ...): Generic function for plotting of R objects. For more details about the graphical parameter arguments, see par.

For simple scatter plots, plot.default will be used. However, there are plot methods for many R objects, including functions, data.frames, density objects, etc. Use methods(plot) and the documentation for these.

type: what type of plot should be drawn. Possible types are.

1. "p" for points,
2. "l" for lines,
3. "b" for both,
4. "c" for the lines part alone of "b",
5. "o" for both ‘overplotted’,
6. "h" for ‘histogram’ like (or ‘high-density’) vertical lines,
7. "s" for stair steps,
8. "S" for other steps, see ‘Details’ below,
9. "n" for no plotting.

The two step types differ in their x-y preference: Going from (x1,y1) to (x2,y2) with x1 < x2, type = "s" moves first horizontal, then vertical, whereas type = "S" moves the other way around.

9种图形如下：

main: an overall title for the plot: see title.

sub: a sub title for the plot: see title.

xlab: a title for the x axis: see title.

ylab: a title for the y axis: see title.

asp: the y/x aspect ratio, see plot.window.（x和y的长宽比）

我们可以通过修改称为图形参数的选项来自定义一幅图形的多个特征（字体、颜色、坐标轴、标签）。一种方法是通过函数par()来指定这些选项。以这种方式设定的参数值除非被再次修改，否则将在会话结束前一直有效。

• par(..., no.readonly = FALSE)

par can be used to set or query（查询） graphical parameters. Parameters can be set by specifying them as arguments to par in tag = value form, or by passing them as a list of tagged values.（通过tag=value传递或者通过标记列表传递）

no.readonly: logical; if TRUE and there are no other arguments, only parameters are returned which can be set by a subsequent par() call on the same device.

adj	The value of adj determines the way in which text strings are justified in text, mtext and title. A value of 0 produces left-justified text, 0.5 (the default) centered text and 1 right-justified text. (Any value in [0, 1] is allowed.) Note that the adj argument of text also allows adj = c(x, y) for different adjustment in x- and y- directions. 确定文本和标题的对齐方式，0~1之间。
ann	If set to FALSE, high-level plotting functions calling plot.default do not annotate the plots they produce with axis titles and overall titles. The default is to do annotation.
ask	logical. If TRUE (and the R session is interactive) the user is asked for input, before a new figure is drawn. 在绘图前对用户进行提醒。
bg	The color to be used for the background of the device region. When called from par() it also sets new = FALSE.  可以通过颜色下标、颜色名称、十六进制的颜色值、RGB值或HSV值来指定颜色。举例来说，col=1、col="white"、col="#FFFFFF"、col=rgb(1,1,1)和col=hsv(0,0,1)都是表示白色的等价方式。
bty	A character string which determined the type of box which is drawn about plots. If bty is one of "o" (the default), "l", "7", "c", "u", or "]" the resulting box resembles the corresponding upper case letter. A value of "n" suppresses the box.  边框形状通过形状相似的字母或数字来定义，"n"代表没有边框。
cex	A numerical value giving the amount by which plotting text and symbols should be magnified relative to the default. This starts as 1 when a device is opened, and is reset when the layout is changed. 图形放大倍数。
cex.axis	The magnification to be used for axis annotation relative to the current setting of cex.
cex.lab	The magnification to be used for x and y labels relative to the current setting of cex.
cex.main	The magnification to be used for main titles relative to the current setting of cex.
cex.sub	The magnification to be used for sub-titles relative to the current setting of cex.
cin	R.O.; character size (width, height) in inches.  只读！ > par()$cin [1] 0.15 0.20
col	A specification for the default plotting color.
col.axis	The color to be used for axis annotation. Defaults to "black".
col.lab	The color to be used for x and y labels. Defaults to "black".
col.main	The color to be used for plot main titles. Defaults to "black".
col.sub	The color to be used for plot sub-titles. Defaults to "black".
cra	R.O.; size of default character (width, height) in ‘rasters’ (pixels). > par()$cra [1] 14.4 19.2