[R] Can't compute row means of two columns of a dataframe.

[Bert Gunter]

Use apply(), not by().

xxxz$av20 <- apply(xxxz[,c("Low20","High20")],1, mean)

-- Bert

On Sat, Jun 8, 2024 at 10:38 AM Sorkin, John <jsorkin using som.umaryland.edu>
wrote:

> I have a data frame with three columns, TotalInches, Low20, High20. For
> each row of the dataset, I am trying to compute the mean of Low20 and
> High20.
>
> xxxz <- structure(list(TotalInches =
>                  c(58, 59, 60, 61, 62, 63, 64, 65,
>                    66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76), Low20 =
> c(84, 87,
>                    90, 93, 96, 99, 102, 106, 109, 112, 116, 119, 122, 126,
> 129,
>                    133, 137, 141, 144), High20 = c(111, 115, 119, 123,
> 127, 131,
>                    135, 140, 144, 148, 153, 157, 162, 167, 171, 176, 181,
> 186, 191
>                    )), class = "data.frame", row.names = c(NA, -19L))
> xxxz
> str(xxxz)
> xxxz$Average20 <- by(xxxz[,c("Low20","High20")],xxxz[,"TotalInches"],mean)
> warnings()
>
> When I run the code above, I don't get the means by row. I get the
> following warning messages, one for each row of the dataframe.
>
> Warning messages:
> 1: In mean.default(data[x, , drop = FALSE], ...) :
>   argument is not numeric or logical: returning NA
> 2: In mean.default(data[x, , drop = FALSE], ...) :
>   argument is not numeric or logical: returning NA
>
>  Can someone tell my what I am doing wrong, and how I can compute the row
> means?
>
> 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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