날짜 시간 데이터 strptime - smart1004/r_lan GitHub Wiki
strptime
시간데이터
milliseconds
https://stackoverflow.com/questions/10931972/r-issue-with-rounding-milliseconds
https://rdrr.io/r/base/as.POSIXlt.html
https://stackoverflow.com/questions/22037657/milliseconds-in-posixct-class
https://statkclee.github.io/data-science/ds-date-basics.html
Date-Time Conversion Function in R