Hello!I am having a problem with Random sampling in R. I have used a syntax: mydata.sub=sample(mydata,7,replace=FALSE,prob=NULL) which allows me to choose a random sample based on the variables(correct me if I am wrong!). Suppose I have 10 variable and if I use the above mentioned command then it will choose 7 variables out of the 10 randomly. My problem is that I want to have a random sample which is not based on the variables but on the values of the variables that is the random sample will be based on the observations. It will be great if someone can help me out me out with a proper syntax. Thanks in Advance. -- View this message in context: http://www.nabble.com/Random-sampling-based-on-the-observations-tp22673975p22673975.html Sent from the R help mailing list archive at Nabble.com.
On Tuesday 24 March 2009, you wrote:> Hello!I am having a problem with Random sampling in R. I have used a > syntax: mydata.sub=sample(mydata,7,replace=FALSE,prob=NULL) which allows me > to choose a random sample based on the variables(correct me if I am > wrong!).Actually, no. You are sampling from a vector, and where you're using the sampled values (on the rows or on the variables) is up to you. Let's say we have a dataset with 100 cases and 10 variables: Case 1: mydata.sub <- mydata[ , sample(10, 7)] This will sample 7 variables out of 10. Case 2: mydata.sub <- mydata[sample(100, 10), ] This will sample 10 cases out of 100.> Suppose I have 10 variable and if I use the above mentioned > command then it will choose 7 variables out of the 10 randomly. My problem > is that I want to have a random sample which is not based on the variables > but on the values of the variables that is the random sample will be based > on the observations. It will be great if someone can help me out me out with > a proper syntax. Thanks in Advance.I think you need to read the help for: ?"[" and most probably one of the introductory books for R. I hope this helps, Adrian -- Adrian Dusa Romanian Social Data Archive 1, Schitu Magureanu Bd. 050025 Bucharest sector 5 Romania Tel.:+40 21 3126618 \ +40 21 3120210 / int.101 Fax: +40 21 3158391 [[alternative HTML version deleted]]
Arup wrote:> Hello!I am having a problem with Random sampling in R. I have used a syntax: > mydata.sub=sample(mydata,7,replace=FALSE,prob=NULL) which allows me to > choose a random sample based on the variables(correct me if I am wrong!). > Suppose I have 10 variable and if I use the above mentioned command then it > will choose 7 variables out of the 10 randomly. My problem is that I want to > have a random sample which is not based on the variables but on the values > of the variables that is the random sample will be based on the > observations. It will be great if someone can help me out me out with a > proper syntax. Thanks in Advance.mydata[sample(nrow(mydata), 7),] Uwe Ligges