[R] Locating data source error in large file

[Rich Shepard]

   The structure of the dataframe is

str(wy2016)
'data.frame':	8784 obs. of  4 variables:
  $ date  : chr  "2015-10-01" "2015-10-01" "2015-10-01" "2015-10-01" ...
  $ time  : chr  "00:00" "01:00" "02:00" "03:00" ...
  $ elev  : num  90.7 90.7 90.7 90.7 90.7 ...
  $ myDate: Date, format: "2015-10-01" "2015-10-01" ...

   The command and results on this dataframe is:
wy2016$myTime <- as.POSIXct(paste(wy2016$date, wy2016$time))
Error in as.POSIXlt.character(x, tz, ...) :
   character string is not in a standard unambiguous format

   Data for other water years do not throw this error. How can I identify
which row(s) among the 8784 have a date or time formatting error?

Rich