R 简明教程

R - Boxplots

箱形图是衡量数据集中的数据分布状况的指标。它将数据集分成三个四分位数。此图表代表了数据集中最小值、最大值、中位数、第一四分位数和第三四分位数。它还可以通过绘制每个数据集的箱形图来比较不同数据集中的数据分布。

Boxplots are a measure of how well distributed is the data in a data set. It divides the data set into three quartiles. This graph represents the minimum, maximum, median, first quartile and third quartile in the data set. It is also useful in comparing the distribution of data across data sets by drawing boxplots for each of them.

在 R 中使用 boxplot() 函数创建箱形图。

Boxplots are created in R by using the boxplot() function.

Syntax

在 R 中创建箱形图的基本语法为 -

The basic syntax to create a boxplot in R is −

boxplot(x, data, notch, varwidth, names, main)

以下是所用参数的描述 -

Following is the description of the parameters used −

  1. x is a vector or a formula.

  2. data is the data frame.

  3. notch is a logical value. Set as TRUE to draw a notch.

  4. varwidth is a logical value. Set as true to draw width of the box proportionate to the sample size.

  5. names are the group labels which will be printed under each boxplot.

  6. main is used to give a title to the graph.

Example

我们使用 R 环境中可用的数据集“mtcars”来创建一个基本的箱形图。我们来看看 mtcars 中的“mpg”和“cyl”列。

We use the data set "mtcars" available in the R environment to create a basic boxplot. Let’s look at the columns "mpg" and "cyl" in mtcars.

input <- mtcars[,c('mpg','cyl')]
print(head(input))

当我们执行以上代码时，会产生以下结果 -

When we execute above code, it produces following result −

                   mpg  cyl
Mazda RX4         21.0   6
Mazda RX4 Wag     21.0   6
Datsun 710        22.8   4
Hornet 4 Drive    21.4   6
Hornet Sportabout 18.7   8
Valiant           18.1   6

Creating the Boxplot

下面的脚本将创建一个反映 mpg（每加仑英里）和 cyl（气缸数）之间的关系的箱形图。

The below script will create a boxplot graph for the relation between mpg (miles per gallon) and cyl (number of cylinders).

# Give the chart file a name.
png(file = "boxplot.png")

# Plot the chart.
boxplot(mpg ~ cyl, data = mtcars, xlab = "Number of Cylinders",
   ylab = "Miles Per Gallon", main = "Mileage Data")

# Save the file.
dev.off()

当我们执行上述代码时，会产生以下结果 -

When we execute the above code, it produces the following result −

boxplot

Boxplot with Notch

我们可以绘制带缺口的箱形图，以找出不同数据组的中位数如何彼此匹配。

We can draw boxplot with notch to find out how the medians of different data groups match with each other.

下面的脚本将为每个数据组创建一个带有缺口的箱形图。

The below script will create a boxplot graph with notch for each of the data group.

# Give the chart file a name.
png(file = "boxplot_with_notch.png")

# Plot the chart.
boxplot(mpg ~ cyl, data = mtcars,
   xlab = "Number of Cylinders",
   ylab = "Miles Per Gallon",
   main = "Mileage Data",
   notch = TRUE,
   varwidth = TRUE,
   col = c("green","yellow","purple"),
   names = c("High","Medium","Low")
)
# Save the file.
dev.off()

当我们执行上述代码时，会产生以下结果 -

When we execute the above code, it produces the following result −

boxplot with notch