Hi,

I have a list/data.frame 'pk' of POSIXct dates, and I'd like to extract the
hour for each row.  I know that if I have an individual POSIXct object, I
can extract the hour by converting to a new object with:

new.lt <- as.POSIXlt(<single POSIXct object>)
new.lt$hour

But I can't figure out how to apply this for a list of such dates in a
vectorized form.  I can write a loop, I guess and implement this, but I
think I'm missing a way that takes advantage of vectorization.  Here is my
loop to just print the hour extracts:

for (ct in pk) {
    lt <- as.POSIXlt(ct, origin="1970-01-01")
    print(lt$hour)
}

So is there a shorter vectorization idiom that lets me do this?  I can't
figure out how to use 'lapply' to apply the '$' operator...

Thanks,
Matt

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