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- 判断变量的属性
is.character(x) #判断是否为字符型
is.numeric(x) #判断是否为数值型
is.vector(x) #判断是否为一个向量
is.matrix(x) #判断是否为一个矩阵
is.array(x) #判断是否为一个数组
is.data.frame(x) #判断是否为一个数据框
- 创建一个矩阵
matrix(data = NA, nrow = 1, ncol = 1, byrow = FALSE, dimnames = NULL)
> x <- matrix(1:20,nrow=5,ncol=4,byrow=T)
> x
[,1] [,2] [,3] [,4]
[1,] 1 2 3 4
[2,] 5 6 7 8
[3,] 9 10 11 12
[4,] 13 14 15 16
[5,] 17 18 19 20
> is.matrix(x)
[1] TRUE
> dim(x) #查看或设置数组的维度向量
[1] 5 4
注意:此时不可以再向dim(x)赋值,如:dim(x) <- c(6,4) ,会有如下报错:
Error in dim(x) <- c(4, 4) : dims [product 16] 因为与对象长度[20]不匹配
但是,可以这样使用:
> x <- 1:20
> dim(x) <- c(5,4)
> x
[,1] [,2] [,3] [,4]
[1,] 1 6 11 16
[2,] 2 7 12 17
[3,] 3 8 13 18
[4,] 4 9 14 19
[5,] 5 10 15 20
> attributes(x) #使用attributes()函数将返回一个列表,其中的第一个元素是dim,dim中包含向量(5,4)
$`dim`
[1] 5 4
还可以利用cbind()和rbind()函数来创建矩阵
> x<-1:3
> x
[1] 1 2 3
> y<-10:12
> y
[1] 10 11 12
> cbind(x,y)
x y
[1,] 1 10
[2,] 2 11
[3,] 3 12
> rbind(x,y)
[,1] [,2] [,3]
x 1 2 3
y 10 11 12
提取对角线元素
> diag(x)
将一个矩阵变成上三角矩阵
> x[lower.tri(y)]<-NA
将一个矩阵变成下三角矩阵
> x[upper.tri(y)]<-NA
- 创建一个列表
列表是可以包含多种类型的对象的向量。
> x<-list(1,"A",FALSE,5+6i)
> x
[[1]]
[1] 1
[[2]]
[1] "A"
[[3]]
[1] FALSE
[[4]]
[1] 5+6i
#列表还可以这样访问
> x[1]
[[1]]
[1] 1
> x[2]
[[1]]
[1] "A"
> x[3]
[[1]]
[1] FALSE
> x[4]
[[1]]
[1] 5+6i
- 创建一个数组
array(data = NA, dim = length(data), dimnames = NULL)
> x<-array(2:6,c(2,4)) #生成一个数值在2到6之间的数组,这个数组为两行四列
> x
[,1] [,2] [,3] [,4]
[1,] 2 4 6 3
[2,] 3 5 2 4
- 将矩阵转换为数据框
as.data.frame(x)
- 查看或设置行名
rownames(x)
rownames(x) <- c(‘a’,’b’,’c’,’d’,’e’)
- 查看或设置列名
colnames(x)
colnames(x) <- c(‘a’,’b’,’c’,’d’,’e’)
- 求行的加和
rowSums(x)
- 数据读取
常用read.table() 和reas.csv()
read.table(file, header = FALSE, sep = "", quote = "\"'",
dec = ".", numerals = c("allow.loss", "warn.loss", "no.loss"),
row.names, col.names, as.is = !stringsAsFactors,
na.strings = "NA", colClasses = NA, nrows = -1,
skip = 0, check.names = TRUE, fill = !blank.lines.skip,
strip.white = FALSE, blank.lines.skip = TRUE,
comment.char = "#",
allowEscapes = FALSE, flush = FALSE,
stringsAsFactors = default.stringsAsFactors(),
fileEncoding = "", encoding = "unknown", text, skipNul = FALSE)
read.csv(file, header = TRUE, sep = ",", quote = "\"",
dec = ".", fill = TRUE, comment.char = "", ...)
read.csv(file.choose()) #在文件目录中选择需要的文件
- 数据写入
write.table(x, file = "", append = FALSE, quote = TRUE, sep = " ",
eol = "\n", na = "NA", dec = ".", row.names = TRUE,
col.names = TRUE, qmethod = c("escape", "double"),
fileEncoding = "")
write.csv()和write.csv2()用法与write.table()相似