¿Cuál es el propósito del formato de hora POSIXct?

What is the purpose of the POSIXct time format?

POSIXct stores date and time in seconds with the number of seconds beginning at 1 January 1970. Negative numbers are used to store dates prior to 1970. Thus, the POSIXct format stores each date and time a single value in units of seconds. Storing the data this way, optimizes use in data.

Class “POSIXct” represents the (signed) number of seconds since the beginning of 1970 (in the UTC time zone) as a numeric vector. Class “POSIXlt” is a named list of vectors representing sec. 0–61: seconds.

Date objects in R Date objects are stored in R as integer values, allowing for dates to be compared and manipulated as you would a numeric vector. Logical comparisons are a simple. When referring to dates, earlier dates are “less than” later dates.

You can use the as. Date( ) function to convert character data to dates. The format is as. Date(x, “format”), where x is the character data and format gives the appropriate format.

Thus, the POSIXct format stores each date and time a single value in units of seconds. Storing the data this way, optimizes use in data.frames and speeds up computation, processing and conversion to other formats. Here we see the number of seconds from 1 January 1970 to 9 October 2015 ( 1445271300 ).

Any conversion that needs to go between the two date-time classes requires a time zone: conversion from “POSIXlt” to “POSIXct” will validate times in the selected time zone. One issue is what happens at transitions to and from DST, for example in the UK

An additional tip to the above initialization: If you begin rbind () activities to add rows to this empty data frame, you may encounter an error like the following if you follow this pattern: I finally discovered that removing the stringsAsFactors=FALSE allowed for the POSIXct value (both integer time and time zone) to transfer to the target DF.

As far as converting date-time strings to POSIXct, there is no row limit. To diagnose, we’ll probably need to see a small sample of your data that includes rows where the conversion succeeds and where it fails. It would also be helpful to see the exact code you ran to read in the data and convert a column to POSIXct.