Question

My Code is reading in a CSV file and converting the time stamp column to the R time format

DF <- read.csv("DF.CSV",head=TRUE,sep=",")

DF[51082,1]
[1] 03/01/2012 19:29


DF[1,1]
[1] 02/24/12 00:29

It reads it in properly and the above 2 rows are displayed as expected

DF$START <- as.POSIXct(strptime(paste(DF$START),format="%m/%d/%y %H:%M"))

DF[1,1]
[1] "2012-02-24 00:29:00 GMT"

DF[51082,1]
[1] NA

After converting them to the R time format using strptime and then displaying them again some of the values have NA and there was no error message displayed or reason for it that I can figure out

Answer 1

You have (at least) two different date formats,
one in %Y (4-digit years), one in %y (2-digit years).
Unless 12 really means 12AD, you need to try both.

DF <- data.frame( 
  START = c(
    "03/01/2012 19:29",
    "02/24/12 00:29"
  ), 
  stringsAsFactors = FALSE 
)
coalesce <- function (x, ...) {
  z <- class(x)
  for (y in list(...)) {
    x <- ifelse(is.na(x), y, x)
  }
  class(x) <- z
  x
}
DF$START <- coalesce(
  as.POSIXct(strptime(DF$START, format="%m/%d/%y %H:%M")),
  as.POSIXct(strptime(DF$START, format="%m/%d/%Y %H:%M"))
)
#                 START
# 1 2012-03-01 19:29:00
# 2 2012-02-24 00:29:00