Re: [R] How to reference or sort rownames in a data frame Thanks, Gabor. I have to say I wouldn't have figured this out easily. I'd summarize your comments by: 1. Remember to use arrays of logicals as indices. 2. Remember %in% for combination matches. 3. Remember which() to get indices. It is the small tasks which appear most difficult to figure out in R. At 10:29 PM 5/27/2007, Gabor wrote: >On 5/27/07, Robert A. LaBudde  wrote: >>As I was working through elementary examples, I was using dataset >>"plasma" of package "HSAUR". >> >>In performing a logistic regression of the data, and making the >>diagnostic plots (R-2.5.0) >> >>data(plasma,package='HSAUR') >>plasma_1<- glm(ESR ~ fibrinogen * globulin, data=plasma, family=binomial()) >>layout(matrix(1:4,nrow=2)) >>plot(plasma_1) >> >>I find that data points corresponding to rownames 17 and 23 are >>outliers and high leverage. >> >>I would then like to perform a fit without these two rows. >> >>In principle this should be easy, using an update() with subset=-c(17,23). >> >>The problem is that the rownames in this dataset are not ordered, >>and, in fact, the relevant rows are 30 and 31, not 17 and 23. >> >>This brings up the following (elementary?) questions: >> >>1. How do you reference rows in "subset=" for which you know the >>rownames, but not the row numbers? > >Use a logical vector: > >   rownames(plasma) %in% c(17, 23) > >> >>2. How do you discovery the rows corresponding to particular >>rownames? (Using plasma[rownames(plasma)==17,] shows the data, but >>NOT the row number!) (Probably the same answer as in Q. 1 above.) > >  which(rownames(plasma) %in% c(17, 23)) # 30, 31 > >> >>3. How do you sort (order) the rows of an existing data frame so that >>the rownames are in order? > > >  plasma[order(as.numeric(rownames(plasma))), ] ================================================================ Robert A. LaBudde, PhD, PAS, Dpl. ACAFS  e-mail: ral@lcfltd.com Least Cost Formulations, Ltd.            URL: http://lcfltd.com/ 824 Timberlake Drive                     Tel: 757-467-0954 Virginia Beach, VA 23464-3239            Fax: 757-467-2947 "Vere scire est per causas scire" ______________________________________________ R-help@stat.math.ethz.ch 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.