Using lapply with variable argument lists - r

Question

Oh man I feel dumb. This is beginner central, but I'm totally lost trying to figure out how to subset arguments in lapply. At this point I've just been randomly trying different combinations of [[ and friends, cursing my clumsiness with the debugging in RStudio.
The issue: I have a dataset collected from SQL Server which includes several columns of date data. Some of these are legitimate datetime values, others are strings. Most have (valid) missing data and some have more than one format. Often the date 1900-01-01 is used as a substitute for NULL. I'm trying very, very hard to be idiomatic and concise in solving this instead of brute forcing it with copy/paste invocations.
My ParseDates() function seems to work well if called column-by-column, but I can't get it to work with lapply. I can see that I'm sending the whole list of orders and threshold values when I only want to pass the current observation, but I can't get my head around how lapply iterates or how to align multiple lists so that the right arguments go with the right call.
I need to finish with all values correctly held as dates (or POSIXct in this instance) with anything close to 1900-01-01 set to NA.
library(lubridate)
# build sample data extract
events <-
structure(
list(
ReservationDate = structure(
c(4L, 2L, 3L, NA,
1L), .Label = c(
"18/12/2006", "1/1/1900", "May 11 2004 12:00AM",
"May 17 2004 12:00AM"
), class = "factor"
), OrigEnquiryDate = structure(
c(1094565600,
937404000, 1089295200, NA, NA), class = c("POSIXct", "POSIXt"), tzone = ""
), UnconditionalDate = structure(
c(1092146400, 935676000,
1087740000, NA, 1168952400), class = c("POSIXct", "POSIXt"), tzone = ""
),
ContractsExchangedDate = structure(
c(NA, NA, NA, NA, 1171544400), class = c("POSIXct", "POSIXt"), tzone = ""
)
), .Names = c(
"ReservationDate",
"OrigEnquiryDate", "UnconditionalDate", "ContractsExchangedDate"
), row.names = c(54103L, 54090L, 54057L, 135861L, 73433L), class = "data.frame"
)
ParseDates <- function(x, orders=NULL, threshold=10) {
# converts to POSIXct if required and replaces 1900-01-01 or similar with na
if(!is.null(orders)) {
x <- parse_date_time(x, orders)
}
x[abs(difftime(x, as.POSIXct("1900-01-01"), units="days")) < threshold] <- NA
return(x)
}
# only consider these columns
date.cols <- names(events) %in% c(
"ReservationDate", "UnconditionalDate", "ContractsExchangedDate", "OrigEnquiryDate"
)
# columns other than these should use the default threshold of 10
date.thresholds <- list("UnconditionalDate"=90, "ContractsExchangedDate"=400)
# columns *other* than these should use the default order of NULL,
# they skip parsing and go straight to threshold testing
date.orders <- list(
"SettlementDate"=c("dmY", "bdY I:Mp"),
"ReservationDate"=c("dmY", "bdY I:Mp")
)
events[date.cols] <- lapply(events[date.cols],
ParseDates(events[date.cols],
orders = date.orders,
threshold = date.thresholds))