0、可以說R語言中一切結構體的基礎是vector！
R中一切都是vector，vecotor的每個component必須類型一致（character,numeric,integer....）！
vector 是沒有dimensions的也沒有attributes，所以去掉dimension和attributes就成了vector（其實dimension可以作為attributes的一個屬性存在但是named** 命名**一般不會作為attributes的屬性的）
解釋下
0.1為何沒有dimensions？
------這里其實糾正我一個觀點：我一直以一個點是有維度的，但其實點是標量
What I don't understand is why vectors (with more than one value) don't have dimensions. They look like they do have 1 dimension. For me no dimension 沒有dimension就是標量,比如一個點就是標量. Like in geometry: a point has no dimension, a line has 1, a square has 2, a cube 3 and so on. Is it because of some internal process? The intuitive geometry way of thinking is not programmatically relevant?
0.2、沒有attributes，如果加了attributes怎么樣？
factors是character data，但是要編碼成 numeric mode，每個number 關聯一個指定的string，稱為levels。比如
1 > fac<- factor(c("b", "a", "b")) 2 > dput(fac) 3 structure(c(2L, 1L, 2L), .Label = c("a", "b"), class = "factor") 4 > levels(fac) 5 [1] "a" "b" 6 > fac 7 [1] b a b 8 Levels: a b 9 > as.numeric(fac) 10 [1] 2 1 2 11 factor組成： integer vector+ levels attributes
1、arrary和vecotr的轉換
if we remove dimension part array just a vector----array去掉屬性dimension就是vector
>nota=array(1:4,4)//只有一個dimension 的array >dim(not1)<-NULL >dput(nota) 1:4 >is.array(nota) >is.vector(nota)
2、array和matrix的轉換
arrays are matrices with more than 2 dimensions.<==>matrices are arrays with only 2 dimensions
Arrays can have any number of dimensions including 1, 2, 3, etc.
比如只有一個維度的array nota=array(1:4,4)
3、list和vecotor的轉換a list with no attributes is a vecotor，所以如下沒有設置屬性的list是vector 的
> vl<- list(sin, 3, "a") > is.vector(vl) [1] TRUE > class(vl) [1] "list" > attributes(vl) NULL 注意names 不是屬性的，所以namedlist依舊是vector > my.list <- list(num=1:3, let=LETTERS[1:2]) > names(my.list) [1] "num" "let" > is.vector(my.list) [1] TRUE