[R] Row median of Date class variables in a data frame

Stephen D. Weigand weigand.stephen at charter.net
Thu Feb 24 05:00:55 CET 2005

I am trying to calculate the median of each row of a
data frame where the data frame consist of
columns of class Date.

Below are my test data and best attempt at using apply.
I didn't see a solution via Google or the Baron search

I'd be grateful for any suggestions or solutions.
I'm using R 2.0.0 on Mac OS X.

Thank you,

Stephen Weigand

### Test data

date1 <- c(1000, 2000, 3000,4000)
date2 <- date1 + 100
date3 <- date2 + 100

class(date1) <- class(date2) <- class(date3) <- "Date"

test <- data.frame(date1, date2, date3)


### create a function for apply()
medDate <- function(x){
   obj <- unclass(unlist(x))
   med <- median(obj, na.rm = TRUE)
   class(med) <- "Date"

medDate(test$date1) # works
medDate(test[1,])   # works

apply(test, 1, medDate) # gives error: 'need numeric data'
apply(test, 2, medDate) # gives error: 'need numeric data'

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