在 R 编程中反转对象的值 - rev()函数

R 语言中的rev()函数用于返回数据对象的反向版本。数据对象可以定义为向量、按列和按行的数据框等。

Syntax: rev(x)

Parameter:
x: Data object

Returns: Reverse of the data object passed

示例 1：

# R program to reverse a vector
  
# Create a vector
vec <- 1:5                           
vec  
  
# Apply rev() function to vector    
vec_rev <- rev(vec)                      
vec_rev                                  

输出：

[1] 1 2 3 4 5
[1] 5 4 3 2 1

示例 2：数据框的反转列

# R program to reverse 
# columns of a Data Frame
  
# Creating a data.frame
data <- data.frame(x1 = 1:5,            
                   x2 = 6:10,
                   x3 = 11:15)
data 
   
# Print reversed example data frame
data_rev <- rev(data)                    
data_rev

输出：

x1 x2 x3
1  1  6 11
2  2  7 12
3  3  8 13
4  4  9 14
5  5 10 15
 
  x3 x2 x1
1 11  6  1
2 12  7  2
3 13  8  3
4 14  9  4
5 15 10  5

示例 3：数据帧的反向行

# R program to reverse
# rows of a data frame
  
# Creating a data frame
data <- data.frame(x1 = 1:5,            
                   x2 = 6:10,
                   x3 = 11:15)
data 
   
# Calling rev() & apply() functions combined
data_rev_row_a <- apply(data, 2, rev)    
data_rev_row_a 
  
# Alternative without rev()  
data_rev_row_b <- data[nrow(data):1, ]   
data_rev_row_b

输出：

x1 x2 x3
1  1  6 11
2  2  7 12
3  3  8 13
4  4  9 14
5  5 10 15
     x1 x2 x3
[1,]  5 10 15
[2,]  4  9 14
[3,]  3  8 13
[4,]  2  7 12
[5,]  1  6 11
  x1 x2 x3
5  5 10 15
4  4  9 14
3  3  8 13
2  2  7 12
1  1  6 11