R语言 反转一个对象的值 – rev()函数
R语言中的 rev() 函数是用来返回数据对象的反向版本。数据对象可以定义为矢量、按列和按行的数据框架等。
语法: rev(x)
参数:
x: 数据对象
返回: 所传递的数据对象的反面
例子 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
例2: 反转数据框架的列
# 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
例3: 反转数据框的行数
# 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