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

[Bert Gunter]

Incidentally, FWIW, for means, rowMeans() is a lot faster:

xxxz$av20 <- rowMeans(xxxz[,c("Low20","High20")])

Bert



On Sat, Jun 8, 2024 at 10:47 AM Bert Gunter <bgunter.4567 using gmail.com> wrote:

> 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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>>
>

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