Re: [R] aggregate function does not work: arguments must have same length

Rui Barradas Sat, 28 Feb 2026 00:41:40 -0800

Às 05:08 de 28/02/2026, Sorkin, John escreveu:

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



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Hello,

The problem is not in the input vectors' lengths, it's the output length.

When aggregating, I find it better to use the formula interface.

It avoids the list() call and eventual errors due to as.list() beingmistaken for it.

Also, when using non base packages, please include a call to library()or similar. I had to revise the function for it to work.



# Number of follow-up hours in each day
timediff <- function(x) {
  difftime(dplyr::last(x), dplyr::first(x), units = "hours")
}

aggregate(NewTime ~ Days, inJan, timediff)
#>         Days  NewTime
#> 1 2020-08-14 23 hours
#> 2 2020-08-15 23 hours
#> 3 2020-08-16  1 hours


Alternative versions:

# This is what Peter Daalgard proposed (list, not as.list)
aggregate(inJan[,"NewTime"], list(inJan[,"Days"]), timediff)

# another one
aggregate(inJan[["NewTime"]], list(inJan[["Days"]]), timediff)


# not relevant, but if you ever want just a vector, here it is.
tapply(inJan[,"NewTime"], inJan[,"Days"], timediff)
#> 2020-08-14 2020-08-15 2020-08-16
#>         23         23          1


Hope this helps,

Rui Barradas

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Re: [R] aggregate function does not work: arguments must have same length

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