Parsing a large amount of characters into a POSIXct object
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When trying to parse a large amount of datetime characters into POSXIct objects, it struck me that strftime and as.POSIXct where actually quite slow. When using the parsing functions from lubridate, these where a lot faster. The following benchmark shows this quite nicely.
We have a character vector xi, which contains about 2.3 million elements. When using strftime, this takes about 105 seconds on my MacBook pro:
> xi[1:10] [1] "2015-06-03 16:17:03" "2015-06-03 16:17:36" "2015-06-03 16:18:09" [4] "2015-06-03 16:18:48" "2015-06-03 16:19:21" "2015-06-03 16:19:54" [7] "2015-06-03 16:20:27" "2015-06-03 16:21:00" "2015-06-03 16:21:32" [10] "2015-06-03 16:22:05" > system.time(res <- as.POSIXct(xi)) user system elapsed 104.941 1.054 106.201
If we switch to ymd_hms from lubridate, we get a very large performance increase:
> library(lubridate) > system.time(res <- ymd_hms(xi)) user system elapsed 0.741 0.136 0.878
ymd_hms is about a 120 times faster.
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