R 简明教程

R - Factors

因子是用于对数据进行分类并将其存储为级别的 data 对象。它们可以存储字符串和整数。它们在具有有限数量唯一值（例如“男性”、“女性”和 True、False 等）的列中很有用。它们在用于统计建模的数据分析中很有用。

通过将向量作为输入，使用 factor () 函数创建因子。

Example

# Create a vector as input.
data <- c("East","West","East","North","North","East","West","West","West","East","North")

print(data)
print(is.factor(data))

# Apply the factor function.
factor_data <- factor(data)

print(factor_data)
print(is.factor(factor_data))

当我们执行上述代码时，会产生以下结果 -

[1] "East"  "West"  "East"  "North" "North" "East"  "West"  "West"  "West"  "East" "North"
[1] FALSE
[1] East  West  East  North North East  West  West  West  East  North
Levels: East North West
[1] TRUE

Factors in Data Frame

在创建任何带有文本数据列的数据框架时，R 将文本列视为分类数据，并在其上创建因子。

# Create the vectors for data frame.
height <- c(132,151,162,139,166,147,122)
weight <- c(48,49,66,53,67,52,40)
gender <- c("male","male","female","female","male","female","male")

# Create the data frame.
input_data <- data.frame(height,weight,gender)
print(input_data)

# Test if the gender column is a factor.
print(is.factor(input_data$gender))

# Print the gender column so see the levels.
print(input_data$gender)

当我们执行上述代码时，会产生以下结果 -

  height weight gender
1    132     48   male
2    151     49   male
3    162     66 female
4    139     53 female
5    166     67   male
6    147     52 female
7    122     40   male
[1] TRUE
[1] male   male   female female male   female male
Levels: female male

Changing the Order of Levels

可以通过再次应用 factor 函数并指定新级别顺序来更改因子中级别的顺序。

data <- c("East","West","East","North","North","East","West",
   "West","West","East","North")
# Create the factors
factor_data <- factor(data)
print(factor_data)

# Apply the factor function with required order of the level.
new_order_data <- factor(factor_data,levels = c("East","West","North"))
print(new_order_data)

当我们执行上述代码时，会产生以下结果 -

 [1] East  West  East  North North East  West  West  West  East  North
Levels: East North West
 [1] East  West  East  North North East  West  West  West  East  North
Levels: East West North

Generating Factor Levels

我们可以使用 gl() 函数生成因子级别。它将两个整数作为输入，以指示有多少个级别以及每个级别出现多少次。

Syntax

gl(n, k, labels)

以下是所用参数的描述 -

  1. n 是给出级别数的整数。

  2. k 是一个给出复制量的整数。

  3. labels 是对结果因子水平的标签的向量。

Example

v <- gl(3, 4, labels = c("Tampa", "Seattle","Boston"))
print(v)

当我们执行上述代码时，会产生以下结果 -

Tampa   Tampa   Tampa   Tampa   Seattle Seattle Seattle Seattle Boston
[10] Boston  Boston  Boston
Levels: Tampa Seattle Boston