John, The issue is the `as.list(inJan[,"Days"])` in the call to `aggregate()`. This makes a list with 50 elements. Try `list(inJan[,"Days"])` instead. Note that there is still an error, but now coming from the `timediff()` function and unrelated to `aggregate()`.
Hope this helps. Steve On Saturday, February 28th, 2026 at 12:08 AM, Sorkin, John <[email protected]> wrote: > PLEASE READ THIS ENTIRE MESSAGE. It explains my problem and contains a > reproducible example of the problem. > > I am trying to run an aggregate function. The function produces the following > error message: > ERROR MESSAGE: > Error in aggregate.data.frame(as.data.frame(x), ...) : > arguments must have same length > > Everything beyond this line can be pasted into an R session and run: > > ####Start of code > #I am trying to write a code that will compute the number of hours for which > we have data for each day. > #Here are my data: > > inJan<- > structure(list(NewTime = structure(c(1597363200, 1597366800, > 1597370400, 1597374000, 1597377600, 1597381200, 1597384800, 1597388400, > 1597392000, 1597395600, 1597399200, 1597402800, 1597406400, 1597410000, > 1597413600, 1597417200, 1597420800, 1597424400, 1597428000, 1597431600, > 1597435200, 1597438800, 1597442400, 1597446000, 1597449600, 1597453200, > 1597456800, 1597460400, 1597464000, 1597467600, 1597471200, 1597474800, > 1597478400, 1597482000, 1597485600, 1597489200, 1597492800, 1597496400, > 1597500000, 1597503600, 1597507200, 1597510800, 1597514400, 1597518000, > 1597521600, 1597525200, 1597528800, 1597532400, 1597536000, 1597539600 > ), class = c("POSIXct", "POSIXt"), tzone = "UTC"), Days = > structure(c(18488, > 18488, 18488, 18488, 18488, 18488, 18488, 18488, 18488, 18488, > 18488, 18488, 18488, 18488, 18488, 18488, 18488, 18488, 18488, > 18488, 18488, 18488, 18488, 18488, 18489, 18489, 18489, 18489, > 18489, 18489, 18489, 18489, 18489, 18489, 18489, 18489, 18489, > 18489, 18489, 18489, 18489, 18489, 18489, 18489, 18489, 18489, > 18489, 18489, 18490, 18490), class = "Date")), class = "data.frame", > row.names = c(NA,-50L)) > inJan > names(inJan) > > #I have written a function which finds the number of hours between a last > time last(x) and a first time first(x). > > # Number of follow-up hours in each day > timediff <- function(x) { > difftime(last(x),first(x),units="hours") > } > > #The function I wrote is used in an aggregate function which > # finds the minimum and maximum time in each day, and then > # calls timediff to find the number of hours in each day. > zoop <- aggregate(inJan[,"NewTime"],as.list(inJan[,"Days"]),timediff) > > #When I run the aggregate function I receive and error: > #Error in aggregate.data.frame(as.data.frame(x), ...) : > #arguments must have same length > > #HOWEVER I believe inJan[,"NewTime"] and inJan[,"Days"] have the same length > > llength(inJan[,"NewTime"]) > #[1] 50 > length(inJan[,"Days"]) > #[1] 50 > > #Can someone tell my why the aggregate function thinks the arguments are a > different length? > #### End of code > > 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; > Former 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, Geriatrics and Palliative Medicine, > 10 North Greene Street > GRECC (BT/18/GR) > Baltimore, MD 21201-1524 > Cell phone 443-418-5382 > > > > ______________________________________________ > [email protected] mailing list -- To UNSUBSCRIBE and more, see > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide https://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code. > ______________________________________________ [email protected] mailing list -- To UNSUBSCRIBE and more, see https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide https://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
