Function in a dataframe comparing two column

Question

I have a data frame with three column. I want to apply a function to compare the second and third column, my function will create a new column. With an example :

vin <- c("vin1", "vin2", "vin3", "vin4")
date.fin.obs <- rep(as.Date("2014-07-04"), length(vin))
date.fin <- c(as.Date("2014-07-04"), as.Date("2013-03-21"), as.Date("2013-07-06"),
             as.Date("2014-07-04"))
df <- data.frame(vin, date.fin.obs, date.fin)

CumulSurvivants <- function(x, y){
#   y <- length(x)
  x.num <- as.numeric(x)
  y.num <- as.numeric(y)

#   i <- length(x)
  i <- 0
  if(x.num == y.num){
    return(i)
  }else{
    return(i+1)
  }


}

CumulSurvivants(x = df$date.fin[2], y = df$date.fin.obs[4])

seems to work, but I want to compare the two column row by row, and to write the result of my function in a new column.

Thanks in advance!

@AnandaMahto, i'm lookink for a new column in my data frame where i can see the result of the function for each row — Mostafa90
– Mostafa90, Commented Jul 9, 2014 at 10:34

Martin · Accepted Answer · 2014-07-09 10:37:40Z

1

To compute the date difference, you may simply use

df$difference <- date.fin.obs - date.fin

resulting in

   vin date.fin.obs   date.fin difference
1 vin1   2014-07-04 2014-07-04     0 days
2 vin2   2014-07-04 2013-03-21   470 days
3 vin3   2014-07-04 2013-07-06   363 days
4 vin4   2014-07-04 2014-07-04     0 days

Or, instead of the simple "minus", use any other more specialized date/time function in the same way, possibly with date/time formatting. Also have a look at ?strptime and http://www.statmethods.net/input/dates.html.

answered Jul 9, 2014 at 10:37

Martin

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