I am interested, what "ct" and "lt" (in POSIXct and POSIXlt) mean. Are they some kind of abbreviations? E.g., does "ct" mean "calendar time" and "lt" something else?
I was just looking into this myself and this question came up in my search results.
I've seen several answers to this very question...but they were apparently all wrong! Here is the definitive answer:
POSIXct
The basic POSIX measure of time, calendar time, is the number of seconds since the beginning of 1970, in the UTC timezone (GMT as described by the French).
POSIXlt
The corresponding R class we called POSIXlt (where the ‘lt’ stands for “local time”), which is a list with components as integer vectors, and so can represent a vector of broken-down times. We wanted to keep track of timezones, so where known the timezone is given by an attribute "tzone", the name of the timezone.
Source: R News
I am finally at peace.