From: zhaoxing731 <zhaoxing731_at_yahoo.com.cn>

Date: Tue, 11 Jan 2011 13:32:35 +0800

#the result

> vec

[1] 1 2 5 6 7 9 13 14 15

¸Ï¿ì×¢²áÑÅ»¢³¬´óÈÝÁ¿Ãâ·ÑÓÊÏä?

R-help_at_r-project.org mailing list

https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code. Received on Tue 11 Jan 2011 - 07:24:06 GMT

Date: Tue, 11 Jan 2011 13:32:35 +0800

Hello

Suppose I have a matrix mat=(1:16,2)

[1,] 1 5 9 13 [2,] 2 6 10 14 [3,] 3 7 11 15 [4,] 4 8 12 16

there is a vector end=c(2,3,1,3)

*#coerce the 1st 2 numbers of the 1st column to a vector [1] 1 2
**#coerce the 1st 3 numbers of the 2nd column and append it to the previous vector [1] 1 2 5 6 7
**#coerce the 1st number of the 3rd column and append it to the previous vector [1] 1 2 5 6 7 9
*

#coerce the 1st 3 numbers of the 4th column and append it to the previous vector [1] 1 2 5 6 7 9 13 14 15

#they are specified by vector end

a for loop

mat<-matrix(1:16,4) end<-c(2,3,1,3) vec<-numeric() for (i in 1:4) {vec<-c(vec,mat[1:end[i],i]) }

#the result

> vec

[1] 1 2 5 6 7 9 13 14 15

but when I want to do it to a large dataset, it's inefficiency becomes a problem, so need vectorization

Thank you in advance

Yours sincerely

ZhaoXing

Department of Health Statistics

West China School of Public Health

Sichuan University

No.17 Section 3, South Renmin Road

Chengdu, Sichuan 610041

P.R.China

¸Ï¿ì×¢²áÑÅ»¢³¬´óÈÝÁ¿Ãâ·ÑÓÊÏä?

R-help_at_r-project.org mailing list

https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code. Received on Tue 11 Jan 2011 - 07:24:06 GMT

Archive maintained by Robert King, hosted by
the discipline of
statistics at the
University of Newcastle,
Australia.

Archive generated by hypermail 2.2.0, at Tue 11 Jan 2011 - 10:30:06 GMT.

*
Mailing list information is available at https://stat.ethz.ch/mailman/listinfo/r-help.
Please read the posting
guide before posting to the list.
*