R语言 向量

向量是最基本的R语言数据对象，有六种类型的原子向量。 它们是逻辑，整数，双精度，复杂，字符和原始。

创建向量

单元素向量

即使在R语言中只写入一个值，它也将成为长度为1的向量，并且属于上述向量类型之一。

# Atomic vector of type character.
print("abc");
 
# Atomic vector of type double.
print(12.5)
 
# Atomic vector of type integer.
print(63L)
 
# Atomic vector of type logical.
print(TRUE)
 
# Atomic vector of type complex.
print(2+3i)
 
# Atomic vector of type raw.
print(charToRaw('hello'))

当我们执行上面的代码，它产生以下结果 -

[1] "abc"
[1] 12.5
[1] 63
[1] TRUE
[1] 2+3i
[1] 68 65 6c 6c 6f

多元素向量

对数值数据使用冒号运算符

# Creating a sequence from 5 to 13.
v <- 5:13
print(v)
 
# Creating a sequence from 6.6 to 12.6.
v <- 6.6:12.6
print(v)
 
# If the final element specified does not belong to the sequence then it is discarded.
v <- 3.8:11.4
print(v)

当我们执行上面的代码，它产生以下结果 -

[1]  5  6  7  8  9 10 11 12 13
[1]  6.6  7.6  8.6  9.6 10.6 11.6 12.6
[1]  3.8  4.8  5.8  6.8  7.8  8.8  9.8 10.8

使用sequence (Seq.)序列运算符

# Create vector with elements from 5 to 9 incrementing by 0.4.
print(seq(5, 9, by = 0.4))

当我们执行上面的代码，它产生以下结果 -

[1] 5.0 5.4 5.8 6.2 6.6 7.0 7.4 7.8 8.2 8.6 9.0

使用C()函数

如果其中一个元素是字符，则非字符值被强制转换为字符类型。

# The logical and numeric values are converted to characters.
s <- c('apple','red',5,TRUE)
print(s)

当我们执行上面的代码，它产生以下结果 -

[1] "apple" "red"   "5"     "TRUE" 

访问向量元素

使用索引访问向量的元素。 []括号用于建立索引。 索引从位置1开始。在索引中给出负值会丢弃来自result.TRUE，FALSE或0和1的元素，也可用于索引。

# Accessing vector elements using position.
t <- c("Sun","Mon","Tue","Wed","Thurs","Fri","Sat")
u <- t[c(2,3,6)]
print(u)
 
# Accessing vector elements using logical indexing.
v <- t[c(TRUE,FALSE,FALSE,FALSE,FALSE,TRUE,FALSE)]
print(v)
 
# Accessing vector elements using negative indexing.
x <- t[c(-2,-5)]
print(x)
 
# Accessing vector elements using 0/1 indexing.
y <- t[c(0,0,0,0,0,0,1)]
print(y)

当我们执行上面的代码，它产生以下结果 -

[1] "Mon" "Tue" "Fri"
[1] "Sun" "Fri"
[1] "Sun" "Tue" "Wed" "Fri" "Sat"
[1] "Sun"

向量操作

向量运算

可以添加，减去，相乘或相除两个相同长度的向量，将结果作为向量输出。

# Create two vectors.
v1 <- c(3,8,4,5,0,11)
v2 <- c(4,11,0,8,1,2)
 
# Vector addition.
add.result <- v1+v2
print(add.result)
 
# Vector substraction.
sub.result <- v1-v2
print(sub.result)
 
# Vector multiplication.
multi.result <- v1*v2
print(multi.result)
 
# Vector division.
divi.result <- v1/v2
print(divi.result)

当我们执行上面的代码，它产生以下结果 -

[1]  7 19  4 13  1 13
[1] -1 -3  4 -3 -1  9
[1] 12 88  0 40  0 22
[1] 0.7500000 0.7272727       Inf 0.6250000 0.0000000 5.5000000

向量元素回收

如果我们对不等长的两个向量应用算术运算，则较短向量的元素被循环以完成操作。

v1 <- c(3,8,4,5,0,11)
v2 <- c(4,11)
# V2 becomes c(4,11,4,11,4,11)
 
add.result <- v1+v2
print(add.result)
 
sub.result <- v1-v2
print(sub.result)

当我们执行上面的代码，它产生以下结果 -

[1]  7 19  8 16  4 22
[1] -1 -3  0 -6 -4  0

向量元素排序

向量中的元素可以使用sort()函数排序。

v <- c(3,8,4,5,0,11, -9, 304)
 
# Sort the elements of the vector.
sort.result <- sort(v)
print(sort.result)
 
# Sort the elements in the reverse order.
revsort.result <- sort(v, decreasing = TRUE)
print(revsort.result)
 
# Sorting character vectors.
v <- c("Red","Blue","yellow","violet")
sort.result <- sort(v)
print(sort.result)
 
# Sorting character vectors in reverse order.
revsort.result <- sort(v, decreasing = TRUE)
print(revsort.result)

当我们执行上面的代码，它产生以下结果 -

[1]  -9   0   3   4   5   8  11 304
[1] 304  11   8   5   4   3   0  -9
[1] "Blue"   "Red"    "violet" "yellow"
[1] "yellow" "violet" "Red"    "Blue" 

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