Chapter 17 Datetime

Datetime is a scalar type corresponding to the elements ofDatetimeVector.

17.1 Creating Datetime object

As with Date, Datetime is also created by specifying the number of seconds from 1970-01-01 00:00:00 UTC (Coordinated Universal Time), and by explicitly specifying the date and time.

The format to explicitly specify the date and time is Datetime dt(str, format). This format converts the string str to Datetime with the format string format. Please refer to help(strptime) in R for symbols used in the format string.

// Creating Datetime object it with elapsed seconds since 00:00:00 on January 1, 1970
Datetime dt;         // "1970-01-01 00:00:00 UTC"
Datetime dt(10.1);   // "1970-01-01 00:00:00 UTC" + 10.1 sec

// Creating by specifying the date and time
// The default format is "%Y-%m-%d %H:%M:%OS"
// The specified date and time are interpreted as vthe date and time of the local time zone
Datetime dt("2000-01-01 00:00:00");
Datetime dt("2000年1月1日 0時0分0秒", "%Y年%m月%d日 %H時%M分%OS秒");

17.2 Time zone

Datetime internally manages the date and time in seconds (real number) from 1970-01-01 00:00:00 in Coordinated Universal Time (UTC). For example, Datetime dt(10) represents the point after 10 seconds from 1970-01-01 00:00:00 UTC. When this value is returned to R, it is displayed as the time converted to the executed time zone. For example, in Japan, Japan Standard Time (JST) is UTC + 9 hours, so Datetime d(10) will be 1970-01-01 09:00:10 JST.

When creating a Datetime object in the form of Datetime dt(str, format), str is interpreted as the time in the local timezone. For example, if you run Datetime dt(2000-01-01 00:00:00); in Japan Standard Time (JST), the value of 1999-12-31 15:00:00 UTC is set internally.

17.3 Operators

The +, -, <, >, >=, <=, ==, != operators are defined in Datetime.

By using these operators, you can perform addition of seconds (+), difference of datetime (-) in seconds, comparison of datetime (<, <=, >, >=, ==, !=) .

17.4 Member functions

Note: The value output using these member functions is the time interpreted at the time of Coordinated Universal Time. Therefore, it looks different from the date and time of the user’s time zone. (For example, refer to the execution result of the code at the end of this chapter)

17.4.1 getFractionalTimestamp()

Returns the number of seconds (real number) from the base date (1970-01-01 00: 00: 00 UTC).

17.4.2 getMicroSeconds()

Returns the microseconds of the date and time at the Coordinated Universal Time. This value express the value of the second after decimal point in units of microseconds. (i.e. 0.1 second = 100000 microseconds)

17.4.3 getSeconds()

Returns the second of the date and time in Coordinated Universal Time.

17.4.4 getMinutes()

Returns the minute of the date and time in Coordinated Universal Time.

17.4.5 getHours()

Returns the hour of the date and time in Coordinated Universal Time.

###getDay()

Returns the day of the date and time in Coordinated Universal Time.

###getMonth()

Returns the month of the date and time in Coordinated Universal Time.

17.4.6 getYear()

Returns the year of the date and time in Coordinated Universal Time.

###getWeekday()

Returns the day of the week of the date and time in Coordinated Universal Time in int.

1:Sun 2:Mon 3:Tue 4:Wed 5:Thu 6:Sat

17.4.7 getYearday()

Returns the number of the date through the year with January 1st as 1 and December 31st as 365.

17.4.8 is_na()

Returns true if this object is NA.

17.5 Code example

The code example below shows the result of executing in Japan Standard Time (JST) environment.

// [[Rcpp::export]]
Datetime rcpp_datetime(){
    // Creating Datetime object by specifying date and time to
    Datetime dt("2000-01-01 00:00:00");

    // Displaying parts of the Datetime object in Coordinated Universal Time
    Rcout << "getYear " << dt.getYear() << "\n";
    Rcout << "getMonth " << dt.getMonth() << "\n";
    Rcout << "getDay " << dt.getDay() << "\n";

    Rcout << "getHours " << dt.getHours() << "\n";
    Rcout << "getMinutes " << dt.getMinutes() << "\n";
    Rcout << "getSeconds " << dt.getSeconds() << "\n";

    Rcout << "getMicroSeconds " << dt.getMicroSeconds() << "\n";
    Rcout << "getWeekday " << dt.getWeekday() << "\n";
    Rcout << "getYearday " << dt.getYearday() << "\n";
    Rcout << "getFractionalTimestamp " << dt.getFractionalTimestamp() << "\n";

    return dt;
}

Execution result

You can see that the time output is 9 hours before Japan Standard Time (JST).

> rcpp_datetime()
getYear 1999
getMonth 12
getDay 31
getHours 15
getMinutes 0
getSeconds 0
getMicroSeconds 0
getWeekday 6
getYearday 365
getFractionalTimestamp 9.46652e+08
[1] "2000-01-01 JST"