[R] Interpreting the output of str on a data frame created using aggregate function

[Bert Gunter]

I think there may be some confusion here.

************************
4) x which is a 844x7 matrix having value "Good", "Moderate", etc.

Correct.
**********************************
To be clear:
x is a matrix of **integers** (presumably population counts) with 7 columns
with names "Good", "Moderate", ... etc.

Apologies if this was already clear from the above.


-- Bert



On Fri, Jan 24, 2025 at 11:14 AM Duncan Murdoch <murdoch.duncan using gmail.com>
wrote:

> 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
> >
> >
> >
> > ______________________________________________
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>
> ______________________________________________
> R-help using r-project.org mailing list -- To UNSUBSCRIBE and more, see
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
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> and provide commented, minimal, self-contained, reproducible code.
>

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