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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