数据类型转换

test for data type

is.numeric()
is.character()
is.vector()
is.matrix()
is.data.frame()

convert it

as.numeric()
as.character()
as.vector()
as.matrix()
as.data.frame()

vector/matrix/data.frame

	to one long  vector	to matrix	to data frame
from vector	c(x,y)	cbind(x,y) rbind(x,y)	data.frame(x,y)
from matrix	as.vector(mymatrix)		as.data.frame(mymatrix)
from data frame		as.matrix(myframe)