Introduction to Date/Time Data

PV‑WAVE’s date/time feature provides a precise method for creating two-dimensional plots with date/time data represented on the X axis. Once you have generated date/time data, you can create plots that reflect various levels of time intervals. The PLOT procedure automatically draws and labels the date/time axis. Date/Time Plot illustrates a plot with two levels of date/time labeling:

Figure 8-1: Date/Time Plot

The date/time axis is well-suited for the display of data that follows an hourly, daily, weekly, or monthly pattern; financial and meteorological data are two examples of this type of data. By default, PV‑WAVE labels a date/time axis with up to six levels of tick labels that show the time frame of the data that is being displayed.

Read your data from an input file into PV‑WAVE using a command such as DC_READ_FREE, DC_READ_FIXED, READF or READU.

The DC_READ_FIXED and DC_READ_FREE functions can be used with the DT_Template keyword to read data directly into date/time variables. See the descriptions for the DC_READ_FIXED and DC_READ_FREE functions in the PV‑WAVE Reference for detailed information on these routines and examples of their use.

The READU and READF procedures can be used to read dates/times into atomic data types, which must then be converted into date/time variables. For a complete account of these input procedures, see Chapter 9: Working with Data Files in the PV‑WAVE Programmer’s Guide.

If you read your data into PV‑WAVE with the READU or READF procedures, you must use conversion functions to convert the date/time information into date/time variables.

There are four functions that you can use to convert your date/time data: STR_TO_DT, VAR_TO_DT, SEC_TO_DT, and JUL_TO_DT. The function you use depends on the configuration of the data you are reading in. See "Converting Your Data into Date/Time Data" for details.

note

In some instances, your input file may not contain explicit date/time information. You can generate a scalar date/time variable with one of the conversion functions and then use the DTGEN function to create a date/time variable containing an array of date/time structures. See "Generating Date/Time Data" for details. Also see Examples 1, 2, and 3 in "Creating Plots with Date/Time Data".

After you have created date/time data, you may want to alter it. PV‑WAVE provides two functions, DT_ADD and DT_SUBTRACT, to add to or subtract date/time intervals from a date/time variable. You may also want to eliminate holidays and weekends from your data with the CREATE_HOLIDAYS and CREATE_WEEKENDS procedures. For details, see "Manipulating Date/Time Data".

You can plot your date/time data with PLOT or OPLOT. PV‑WAVE automatically generates labels and tick marks for your date/time data. If you want to modify the appearance of the date/time axis, PV‑WAVE provides several keywords. For details, see "Creating Plots with Date/Time Data".