Axes

参考自 cookbook-r (opens new window)

本文档介绍ggplot绘图中对axes的修改。在文档开始之前，先看看ggplot2默认的图例：

library(ggplot2)
bp <- ggplot(data=PlantGrowth, aes(x=group, y=weight, fill=group)) + geom_boxplot()
bp

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# 1. 交换X和Y轴

bp + coord_flip()

# 2. 离散型坐标轴

# 2.1. 改变离散型刻度顺序

# Manually set the order of a discrete-valued axis
bp + scale_x_discrete(limits=c("trt1","trt2","ctrl"))

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只改变坐标轴，不会改变legend

# 2.2. 设置刻度线标签

bp + scale_x_discrete(breaks=c("ctrl", "trt1", "trt2"),
                      labels=c("Control", "Treat 1", "Treat 2"))
					  
# Hide x tick marks, labels, and grid lines
bp + scale_x_discrete(breaks=NULL)

# Hide all tick marks and labels (on X axis), but keep the gridlines
bp + theme(axis.ticks = element_blank(), axis.text.x = element_blank())

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# 3. 连续型坐标轴

# 3.1. 设置坐标轴范围

如果只是简单的想要坐标轴包含范围内的特定值，可以使用 expand_limits()。这只能扩大一个轴的范围；它不能缩小范围。

# Make sure to include 0 in the y axis
bp + expand_limits(y=0)

# Make sure to include 0 and 8 in the y axis
bp + expand_limits(y=c(0,8))

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在这个例子中，bp + expand_limits(y=c(0,5)) 与 bp + expand_limits(y=0) 将得到相同的图，因为原图坐标轴已经包含了5

此外，可以明确的设置坐标轴的上下限，使用ylim 或者 scale_y_continuous，需要注意的是，只要使用了scale_y_continuous，ylim将失效

# Set the range of a continuous-valued axis
# These are equivalent
bp + ylim(0, 8)
# bp + scale_y_continuous(limits=c(0, 8))

bp + ylim(4, 6)
# 如果ylim 不包含全部数据范围，会提示warning信息
# Warning message:
# Removed 6 rows containing non-finite values (stat_boxplot).

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# 3.2. 反转坐标轴方向

# Reverse order of a continuous-valued axis
bp + scale_y_reverse()

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# 3.3. 设置和隐藏刻度

# Setting the tick marks on an axis
# This will show tick marks on every 0.25 from 1 to 10
# 绘制刻度在(3.50-6.25）之间的数据
bp + scale_y_continuous(breaks=seq(1,10,1/4))

# 刻度可以是不均匀的
bp + scale_y_continuous(breaks=c(4, 4.25, 4.5, 5, 6,8))

# 隐藏刻度、和网格线
bp + scale_y_continuous(breaks=NULL)

# 隐藏刻度ticks、刻度标签，但保留网格线
bp + theme(axis.ticks = element_blank(), axis.text.y = element_blank())

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# 3.4. 坐标轴转换(log、sqrt)

坐标轴默认是线性的，也可以对其进行转换（log, power, roots等）

有两种变换轴的方法。一种是使用尺度变换(scale)，另一种是使用坐标变换(coordinate)。

尺度变换，数据变换发生刻度(ticks)、轴范围(range)等属性确定之前;
坐标变换，变换发生刻度(ticks)、轴范围(range)等属性确定之后。

这会导致不同的外观，如下所示。

# Create some noisy exponentially-distributed data
set.seed(201)
n <- 100
dat <- data.frame(
    xval = (1:n+rnorm(n,sd=5))/20,
    yval = 2*2^((1:n+rnorm(n,sd=5))/20)
)

# A scatterplot with regular (linear) axis scaling
sp <- ggplot(dat, aes(xval, yval)) + geom_point()
sp

# log2 scaling of the y axis (with visually-equal spacing)
library(scales)     # Need the scales package
sp + scale_y_continuous(trans=log2_trans())

# log2 coordinate transformation (with visually-diminishing spacing)
sp + coord_trans(y="log2")

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通过比例变换，可以顺便设置坐标轴刻度线和label。

sp + scale_y_continuous(trans = log2_trans(),
                        breaks = trans_breaks("log2", function(x) 2^x),
                        labels = trans_format("log2", math_format(2^.x)))

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# 3.5. 固定x轴和y轴比率

# Data where x ranges from 0-10, y ranges from 0-30
set.seed(202)
dat <- data.frame(
    xval = runif(40,0,10),
    yval = runif(40,0,30)
)
sp <- ggplot(dat, aes(xval, yval)) + geom_point()

# Force equal scaling
sp + coord_fixed()

# Equal scaling, with each 1 on the x axis the same length as y on x axis
sp + coord_fixed(ratio=1/3)

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默认不固定x轴和y轴比率，生成的图可以按照长宽调整形态，而固定之后不管怎么调都不变化。

# 4. 修改坐标轴标签

如果仅改变坐标轴label文本内容，可以通过theme,xlab|ylab, scale_x|y_xxxx, labs 等函数修改。

p1 <- bp + theme(axis.title.x = element_blank()) +   # Remove x-axis label
     ylab("Weight (Kg)")                       # Set y-axis label

p2 <- bp + xlab(NULL) +   # Remove x-axis label
     ylab("Weight (Kg)")                       # Set y-axis label

# p1 与p2等同

# Also possible to set the axis label with the scale
# x轴label为空字符串，垂直方向label空间保留
p3 <- bp + scale_x_discrete(name="") +
     scale_y_continuous(name="Weight (Kg)")

# not show
p4 <- bp + labs(x = NULL, y = "Weight (Kg)")

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使用theme 还可以修改label和刻度的style。

# Change font options:
# X-axis label: bold, red, and 20 points
# X-axis tick marks: rotate 90 degrees CCW, move to the left a bit (using vjust,
#   since the labels are rotated), and 16 points
bp + theme(axis.title.x = element_text(face="bold", colour="#990000", size=20),
           axis.text.x  = element_text(angle=90, vjust=0.5, size=16))

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# 5. 坐标轴刻度格式化输出

格式化坐标轴刻度，e.g. 百分比，科学计数等，可以通过特定的formater完成

# Label formatters
library(scales)   # Need the scales package
bp + scale_y_continuous(labels=percent) +
     scale_x_discrete(labels=abbreviate)  # In this particular case, it has no effect
	 
# Self-defined formatting function for times.
timeHMS_formatter <- function(x) {
    h <- floor(x/60)
    m <- floor(x %% 60)
    s <- round(60*(x %% 1))                   # Round to nearest second
    lab <- sprintf('%02d:%02d:%02d', h, m, s) # Format the strings as HH:MM:SS
    lab <- gsub('^00:', '', lab)              # Remove leading 00: if present
    lab <- gsub('^0', '', lab)                # Remove leading 0 if present
}

bp + scale_y_continuous(label=timeHMS_formatter)

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对于连续型变量的，常用的formatters 还包括comma, percent, dollar, and scientific.
对与离散性变量，abbreviate 将删除元音和空格并缩短为四个字符
对于日期，可以用date_format

# 6. 隐藏网格线

网格线分为major 和 minor

major: 与刻度对应的网格线
minor: 刻度以外的辅助线

# 6.1. 隐藏所有垂直和水平网格线

# Hide all the gridlines
bp + theme(panel.grid.minor=element_blank(),
           panel.grid.major=element_blank())

# Hide just the minor gridlines
bp + theme(panel.grid.minor=element_blank())

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# 6.2. 隐藏垂直或水平网格线

# Hide all the vertical gridlines
bp + theme(panel.grid.minor.x=element_blank(),
           panel.grid.major.x=element_blank())

# Hide all the horizontal gridlines
bp + theme(panel.grid.minor.y=element_blank(),
           panel.grid.major.y=element_blank())

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编辑

#ggplot2 #axes

上次更新: 2021/07/08, 21:34:07

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