R - 向量
向量是最基本的 R 数据对象，有六种类型的Atomics向量。它们是逻辑、整数、双精度、复数、字符和原始。
矢量创建
单元素向量
即使在 R 中只写入一个值，它也会成为长度为 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时，它会产生以下结果 -
[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时，它会产生以下结果 -
[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
使用序列（Seq.）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时，它会产生以下结果 -
[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
如果元素之一是字符，则非字符值将被强制为字符类型。
# 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时，它会产生以下结果 -
[1] "apple" "red" "5" "TRUE"
访问向量元素
使用索引来访问 Vector 的元素。[ ] 括号用于索引。索引从位置 1 开始。在索引中给出负值会将该元素从结果中删除。TRUE、FALSE或0和1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时，它会产生以下结果 -
[1] "Mon" "Tue" "Fri" [1] "Sun" "Fri" [1] "Sun" "Tue" "Wed" "Fri" "Sat" [1] "Sun"
矢量处理
向量运算
两个相同长度的向量可以相加、相减、相乘或相除，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 subtraction. 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时，它会产生以下结果 -
[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
如果我们对两个长度不等的向量进行算术运算，则较短向量的元素将被回收来完成运算。
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时，它会产生以下结果 -
[1] 7 19 8 16 4 22 [1] -1 -3 0 -6 -4 0
向量元素排序
可以使用sort()函数对向量中的元素进行排序。
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时，它会产生以下结果 -
[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"