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
code: mySD <- function(x) {sapply(x,sqrt(var(x)))} class(mySD) by(goop[,c("a","b","c")],goop[,"Arm"],mySD) 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, John 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")) goop mySD <- function(x) {sapply(x,sqrt(var(x)))} class(mySD) by(goop[,c("a","b","c")],goop[,"Arm"],mySD) 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 GRECC (BT/18/GR) Baltimore, MD 21201-1524 (Phone) 410-605-7119 (Fax) 410-605-7913 (Please call phone number above prior to faxing) Confidentiality Statement: This email message, including any attachments, is for the sole use of the intended recipient(s) and may contain confidential and privileged information. Any unauthorized use, disclosure or distribution is prohibited. If you are not the intended recipient, please contact the sender by reply email and destroy all copies of the original message. ______________________________________________ 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 http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.