vector分为两种:

• atomic vectors：向量中仅含一种数据类型;
• lists:向量中含有多种数据类型。

Logical vector

> num_vect <- c(0.5, 55, -10, 6)
> tf <- num_vect < 1
> tf
[1]  TRUE FALSE  TRUE FALSE

Logical condition 有三种: TRUE, FALSE, NA(not availabe).
logical operators有:< , >=,>, <=, == and !=

character vector

> my_char <- c("My", "name", "is")
> my_char
[1] "My"   "name" "is"

> paste(my_char, collapse = " ")
[1] "My name is"
> paste("Hello fdfd fdfd", "world!", sep = ",")
[1] "Hello fdfd fdfd, world!"
> paste(1:3, c("X", "Y", "Z"), sep = "")
[1] "1X" "2Y" "3Z"
> paste(LETTERS, 1:4, sep = "-")
 [1] "A-1" "B-2" "C-3" "D-4" "E-1" "F-2" "G-3" "H-4" "I-1" "J-2" "K-3" "L-4" "M-1"
[14] "N-2" "O-3" "P-4" "Q-1" "R-2" "S-3" "T-4" "U-1" "V-2" "W-3" "X-4" "Y-1" "Z-2"

collapse是对my_char向量内部中每个元素进行分隔，sep是对两个输入向量之间进行分隔，向量内部不进行操作。sep默认参数是" "(即空格)。