Duncan, First, thank you for your prompt, and clear response. Additionally, thank you for being receptive to a question that some people might consider to be unworthy of answering, or replying with a snarky remark. R can be powerful, but it also can be intimidating. Thank you, John
Did I just make a statement worthy of a fortune? John David Sorkin M.D., Ph.D. Professor of Medicine, University of Maryland School of Medicine; Associate Director for Biostatistics and Informatics, Baltimore VA Medical Center Geriatrics Research, Education, and Clinical Center; PI Biostatistics and Informatics Core, University of Maryland School of Medicine Claude D. Pepper Older Americans Independence Center; Senior Statistician University of Maryland Center for Vascular Research; Division of Gerontology and Paliative Care, 10 North Greene Street GRECC (BT/18/GR) Baltimore, MD 21201-1524 Cell phone 443-418-5382 ________________________________________ From: Duncan Murdoch <murdoch.dun...@gmail.com> Sent: Friday, January 24, 2025 2:13 PM To: Sorkin, John; r-help@r-project.org (r-help@r-project.org) Subject: Re: [R] Interpreting the output of str on a data frame created using aggregate function I'll answer your question inline. On 2025-01-24 2:03 p.m., Sorkin, John wrote: > I ran the following code: > marginalcats <- aggregate(meanbyCensusIDAndDay3$cats, > list(meanbyCensusIDAndDay3$CensusID),table) > followed by > str(marginalcats) > > I received the following output: > 'data.frame': 844 obs. of 2 variables: > $ Group.1: num 6e+09 6e+09 6e+09 6e+09 6e+09 ... > $ x : int [1:844, 1:7] 14 14 14 14 14 14 14 14 14 14 ... > ..- attr(*, "dimnames")=List of 2 > .. ..$ : NULL > .. ..$ : chr [1:7] "Good" "Moderate" "Unhealthy For Some" "Unhealthy" ... > > I am trying to understand the output. I believe it says that marginalcats > (1) is a data frame > (2) the df has two elements (I) Group.1 and (II) x Correct so far. > (3) Group.1 is a ?list? of number No, it's a numeric vector. The length doesn't print because it's in a dataframe, so the length is 844, the number of dataframe observations. > (4) x which is a 844x7 matrix having value "Good", "Moderate", etc. Correct. > > A few questions: > (A) Is the interpretation given above correct? > (B) Does the .. ..$ : NULL mean that the matrix has no row names? Yes. > (C) What does "attr(*, "dimnames")=List of 2" mean? That says x has an attribute called "dimnames", which is a list with two elements. They are the row names (which is NULL, you don't have any) and the column names. > (D) Does it mean that the dimensions of the matrix are stored as two separate > lists? No. The dim is an attribute which is shown implicitly as "[1:844, 1:7]", i.e. c(844, 7). Duncan Murdoch > (E) If so, how do I access the lists? > When I enter > dimnames(marginalcatsx$x) > I receive: > > [[1]] > NULL > > [[2]] > [1] "Good" "Moderate" "Unhealthy For Some" > "Unhealthy" "Very Unhealthy" "Hazardous1" > [7] "Hazardous2" > > Thank you, > John > > John David Sorkin M.D., Ph.D. > Professor of Medicine, University of Maryland School of Medicine; > Associate Director for Biostatistics and Informatics, Baltimore VA Medical > Center Geriatrics Research, Education, and Clinical Center; > PI Biostatistics and Informatics Core, University of Maryland School of > Medicine Claude D. Pepper Older Americans Independence Center; > Senior Statistician University of Maryland Center for Vascular Research; > > Division of Gerontology and Paliative Care, > 10 North Greene Street > GRECC (BT/18/GR) > Baltimore, MD 21201-1524 > Cell phone 443-418-5382 > > > > ______________________________________________ > R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide https://www.r-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code. ______________________________________________ R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide https://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
