[R] error using by(goop[, c("a", "b", "c")], goop[, "Arm"], mySD) was Re: by gives no results, gives warning that data are non-numeric, but the data appears to be numeric.

John Sorkin jsorkin at grecc.umaryland.edu
Mon Dec 28 22:54:57 CET 2015

I am  trying to use the by function to get the SD of each column of a data frame, stratified by ARM. Using a suggestion provided by both William Dunlap and Rolf Turner, I have written the code below which fails with the error:
Error in match.fun(FUN) :   'sqrt(var(x))' is not a function, character or symbol

mySD <- function(x) {sapply(x,sqrt(var(x)))}
Below I include code which will create goop (thank you Bill for suggesting I use dput), which will run will recreate mmy error. Any thoughts on why the by function fails and how to fix it would be appreciated.
Thank you,
goop <- structure(c(180L, 153L, 149L, 218L, 217L, 147L, 141L, 141L, 174L, 
                    162L, 163L, 206L, 168L, 227L, 142L, 179L, 270L, 206L, 243L, 134L, 
                    131L, 222L, 142L, 119L, 149L, 190L, 196L, 145L, 185L, 235L, 165L, 
                    246L, 152L, 186L, 222L, 248L, 125L, 149L, 233L, 145L, 154L, 231L, 
                    146L, 161L, 150L, 133L, 115L, 145L, 180L, 202L, 158L, 210L, 153L, 
                    136L, 265L, 255L, 199L, 131L, 110L, 169L, 147L, 133L, 108L, 203L, 
                    185L, 153L, 154L, 207L, 167L, 233L, 135L, 127L, 197L, 245L, 124L, 
                    125L, 146L, 139L, 158L, 211L, 183L, 169L, 137L, 114L, 176L, 143L, 
                    156L, 209L, 163L, 194L, 151L, 238L, 253L, 293L, 208L, 147L, 186L, 
                    179L, 150L, 203L, 112L, 185L, 156L, 127L, 132L, 243L, 177L, 242L, 
                    144L, 140L, 194L, 249L, 109L, 91L, 10163L, 10987L, 19882L, 19899L, 
                    20104L, 20105L, 20167L, 20318L, 20338L, 20392L, 20453L, 20454L, 
                    20467L, 20500L, 20682L, 20687L, 20692L, 20744L, 20750L, 20751L, 
                    20806L, 20848L, 20856L, 20959L, 21023L, 21048L, 21114L, 21134L, 
                    21135L, 21320L, 21329L, 21349L, 21353L, 21521L, 21663L, 21784L, 
                    22031L, 22081L, 2L, 2L, 1L, 1L, 1L, 1L, 1L, 2L, 1L, 1L, 2L, 2L, 
                    2L, 1L, 1L, 2L, 2L, 2L, 1L, 1L, 1L, 1L, 1L, 2L, 1L, 1L, 2L, 1L, 
                    2L, 1L, 2L, 1L, 1L, 1L, 1L, 1L, 2L, 2L), .Dim = c(38L, 5L), .Dimnames = list(
                      NULL, c("a", "b", "c", "ID", "Arm")), na.action = structure(37, class = "omit"))
mySD <- function(x) {sapply(x,sqrt(var(x)))}


John David Sorkin M.D., Ph.D.
Professor of Medicine
Chief, Biostatistics and Informatics
University of Maryland School of Medicine Division of Gerontology and Geriatric Medicine
Baltimore VA Medical Center
10 North Greene Street
Baltimore, MD 21201-1524
(Phone) 410-605-7119
(Fax) 410-605-7913 (Please call phone number above prior to faxing) 

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