R notes[2]

文章目录

• sequence
• references

sequence

1. organized equence is a regular facility of R language,it can be generated by the seq() function.of couse ,in oder to make arbitrary list, the c() is used to achieve the task,that is explained at the previous note.
   the seq funtcion forms as follows.

seq(from_value,to_value,step)

> seq(1,10,2)
[1] 1 3 5 7 9
> seq(1,10,1)
 [1]  1  2  3  4  5  6  7  8  9 10
> seq(1,10,7)
[1] 1 8
> seq(10,1,-1)
 [1] 10  9  8  7  6  5  4  3  2  1

you may assign arguments in keyword,for example, seq(to=1,from=10,by=-1).

the rep function also make sequence which is different from seq,rep puts the same elements together into a list with specified number of times by default.

> rep(-1,3)
[1] -1 -1 -1

> rep(1,each=2)
[1] 1 1
> rep(1,times=2)
[1] 1 1
> rep(1,2)
[1] 1 1

We need to pay attention that if given element is a list,the rep have a argument named each which will repeatedly generate each element of given list for specified number of times and then arrange them in original order of each element .

> a<-c(1,2)
> rep(a,3)
[1] 1 2 1 2 1 2
> rep(a,times=3)
[1] 1 2 1 2 1 2
> rep(a,each=3)
[1] 1 1 1 2 2 2

references

1. https://cran.r-project.org/doc/manuals/