change a column from birth date to age in r

Question

I am using data.table for the first time.

I have a column of about 400,000 ages in my table. I need to convert them from birth dates to ages.

What is the bes

Answer 1

I wasn't happy with any of the responses when it comes to calculating the age in months or years, when dealing with leap years, so this is my function using the lubridate package.

Basically, it slices the interval between from and to into (up to) yearly chunks, and then adjusts the interval for whether that chunk is leap year or not. The total interval is the sum of the age of each chunk.

library(lubridate)

#' Get Age of Date relative to Another Date
#'
#' @param from,to the date or dates to consider
#' @param units the units to consider
#' @param floor logical as to whether to floor the result
#' @param simple logical as to whether to do a simple calculation, a simple calculation doesn't account for leap year.
#' @author Nicholas Hamilton
#' @export
age <- function(from, to = today(), units = "years", floor = FALSE, simple = FALSE) {

  #Account for Leap Year if Working in Months and Years
  if(!simple && length(grep("^(month|year)",units)) > 0){
    df = data.frame(from,to)
    calc = sapply(1:nrow(df),function(r){

      #Start and Finish Points
      st = df[r,1]; fn = df[r,2]

      #If there is no difference, age is zero
      if(st == fn){ return(0) }

      #If there is a difference, age is not zero and needs to be calculated
      sign = +1 #Age Direction
      if(st > fn){ tmp = st; st = fn; fn = tmp; sign = -1 } #Swap and Change sign

      #Determine the slice-points
      mid   = ceiling_date(seq(st,fn,by='year'),'year')

      #Build the sequence
      dates = unique( c(st,mid,fn) )
      dates = dates[which(dates >= st & dates <= fn)]

      #Determine the age of the chunks
      chunks = sapply(head(seq_along(dates),-1),function(ix){
        k = 365/( 365 + leap_year(dates[ix]) )
        k*interval( dates[ix], dates[ix+1] ) / duration(num = 1, units = units)
      })

      #Sum the Chunks, and account for direction
      sign*sum(chunks)
    })

  #If Simple Calculation or Not Months or Not years
  }else{
    calc = interval(from,to) / duration(num = 1, units = units)
  }

  if (floor) calc = as.integer(floor(calc))
  calc
}