Plot Dates and Times
This example shows how to create line plots with dates and times that are stored as
duration arrays. The
datetime data type represents points in time, such as August 24, 2020, 10:50:30 a.m., while the
duration data type represents lengths of time, such as 12 hours and 30 minutes. Most plotting functions accept
duration arrays as x-, y-, and z-coordinates and show tick values with appropriate date and time units. You can specify your own axis limits and tick values using
duration values. You can also change the format of tick values to show date and time units of your choice. Data tips show
duration values for cursor positions on a plot, and you can export those values to workspace variables. When you read data from a spreadsheet or comma-separated value (CSV) file, you can include the date and time data in your plots.
Plot Date and Time Data
You can plot
duration arrays without converting them to numeric arrays. Most plotting functions accept
duration arrays as input arguments.
For example, plot a data set that has
datetime values on the x-axis and numeric values on the y-axis. The x-coordinates are the
datetime values for every day in June and July 2021. The plot automatically displays tick values with an appropriate format on the x-axis. In this case, the appropriate format shows month names and day numbers with the year.
XDates = [datetime(2021,6,1:30) datetime(2021,7,1:31)]; YNumsForXDates = sin(0:0.1:6); plot(XDates,YNumsForXDates)
Similarly, plot a data set that has
duration values on the x-axis. To create a
duration array in units of seconds, use the
XTimes = seconds(0:120); YNumsForXTimes = cos(0:0.05:6); plot(XTimes,YNumsForXTimes)
Specify Axes Limits
When you change the limits on a plot, the tick values that are shown for
duration values are updated automatically. You can update limits interactively or by calling the
zlim functions for the corresponding axis. Specify the new limits as a
duration array. If you change limits to zoom in or zoom out far enough, then the tick values can show other date and time components, not just new tick values.
For example, plot the
YNumsForXDates arrays. Then change the x-axis limits to June 20 and July 7, 2021, using
xlim. The plot displays new tick values.
plot(XDates,YNumsForXDates) xlim([datetime("2021-06-20") datetime("2021-07-07")])
Change the x-axis limits to June 20 and June 22, 2021. The tick values show hour and minute components in hh:mm format because the plot is zoomed in enough to show smaller time units on the x-axis.
Specify Tick Values
You do not have to change axes limits to change tick values. Instead, you can specify your own tick values along the x-, y-, or z-axes by using the
zticks functions. Specify the tick values as a
For example, plot the
YNumsForXTimes arrays. Then specify tick values at 0, 60, and 120 seconds by using
plot(XTimes,YNumsForXTimes) xticks(seconds([0 60 120]))
Specify Tick Format
Plotting functions use default formats to display
duration values as tick values. To override the format for the tick values on an axis, use the
For example, plot
YNumsForXDates. Specify a tick value format showing year, month, and day numbers by using
As an alternative, you can also call
plot with the
DurationTickFormat name-value arguments. For example, this call to the
plot function creates the same plot.
However, these name-value arguments can be used with the
plot function only. You can use functions such as
xtickformat after calling any plotting function, such as
Axes Properties That Store Dates and Times
Axis limits, the locations of tick labels, and the x-, y-, and z-values for
duration arrays in line plots are also stored as properties of an
Axes object. These properties represent those aspects of line plots.
For example, the
XTick properties associated with the plot of
datetime values. Get the
Axes object for the plot and display these properties.
ax = gca; ax.XLim
ans = 1x2 datetime 2021-06-01 2021-08-03
ans = 1x5 datetime 2021-06-01 2021-06-15 2021-06-29 2021-07-13 2021-07-27
Export and Convert Data Tip Values
When you click on a plot, you create a data tip at that cursor position that displays its x- and y-coordinates. Data tips display numeric values as well as
duration values. However, when you export the cursor data to the workspace, the coordinates are reported as a pair of numeric values. To convert exported cursor data to the
duration value, use the
For example, plot
YNumsForXDates. Then create a data tip by clicking on the plot.
To export the cursor data to the workspace, right-click the data tip and select Export Cursor Data to Workspace. This action exports the cursor data to a structure in the workspace.
cursor_info = struct with fields: Target: [1×1 Line] Position: [25 0.5985] DataIndex: 26
cursor_info.Position field represents the cursor data as a pair of numeric values. The
Axes object associated with the plot has the information needed to convert the numeric value of the x-coordinate to a
datetime value. Get the
Axes object for the plot. Then pass the numeric x-coordinate and the x-axis from the
Axes object to
ax = gca; datetimePosition = num2ruler(cursor_info.Position(1),ax.XAxis) datetimePosition = datetime 26-Jun-2021
You do not need to convert the numeric y-coordinate,
cursor_info.Position(2) because the y-values in this plot are numeric.
Plot Dates and Times from File
Data files such as spreadsheets and CSV files often store dates and times as formatted text. When you read in data from such files, you can convert text representing dates and times to
duration arrays. Then you can create plots of that data.
For example, create a plot of data from the example data file
outages.csv. This CSV file contains six columns of data. Two columns contain text that represent dates and times.
Region,OutageTime,Loss,Customers,RestorationTime,Cause SouthWest,2002-02-01 12:18,458.9772218,1820159.482,2002-02-07 16:50,winter storm SouthEast,2003-01-23 00:49,530.1399497,212035.3001,,winter storm SouthEast,2003-02-07 21:15,289.4035493,142938.6282,2003-02-17 08:14,winter storm ...
The recommended way to read data from a CSV file is to use the
readtable function. This function reads data from a file and returns it in a table.
readtable function automatically converts the text in the
RestorationTime columns to
datetime arrays. The columns that represent numbers (
Customers) are read in as numeric arrays. The remaining columns are read in as strings. The table stores the columns of data from
outages.csv in table variables that have the same names. Finally, sort the rows of
T by the dates and times in
OutageTime by using the
sortrows function. If a table is not sorted by time, then it is a best practice to sort the table by time before plotting or analyzing the data.
T = readtable("outages.csv","TextType","string"); T = sortrows(T,"OutageTime")
T=1468×6 table Region OutageTime Loss Customers RestorationTime Cause ___________ ____________________ ______ __________ ____________________ __________________ "SouthWest" 01-Feb-2002 12:18:00 458.98 1.8202e+06 07-Feb-2002 16:50:00 "winter storm" "MidWest" 05-Mar-2002 17:53:00 96.563 2.8666e+05 10-Mar-2002 14:41:00 "wind" "MidWest" 16-Mar-2002 06:18:00 186.44 2.1275e+05 18-Mar-2002 23:23:00 "severe storm" "MidWest" 26-Mar-2002 01:59:00 388.04 5.6422e+05 28-Mar-2002 19:55:00 "winter storm" "MidWest" 20-Apr-2002 16:46:00 23141 NaN NaT "unknown" "SouthWest" 08-May-2002 20:34:00 50.732 34481 08-May-2002 22:21:00 "thunder storm" "MidWest" 18-May-2002 11:04:00 1389.1 1.3447e+05 21-May-2002 01:22:00 "unknown" "NorthEast" 20-May-2002 10:57:00 9116.6 2.4983e+06 21-May-2002 15:22:00 "unknown" "SouthEast" 27-May-2002 09:44:00 237.28 1.7101e+05 27-May-2002 16:19:00 "wind" "SouthEast" 02-Jun-2002 16:11:00 0 0 05-Jun-2002 05:55:00 "energy emergency" "West" 06-Jun-2002 19:28:00 311.86 NaN 07-Jun-2002 00:51:00 "equipment fault" "SouthEast" 17-Jun-2002 23:01:00 42.542 39877 17-Jun-2002 23:49:00 "thunder storm" "MidWest" 01-Jul-2002 04:33:00 203.94 60650 02-Jul-2002 14:54:00 "severe storm" "MidWest" 01-Jul-2002 08:18:00 100.71 1.8116e+05 01-Jul-2002 11:33:00 "severe storm" "MidWest" 10-Jul-2002 01:49:00 168.02 NaN 10-Jul-2002 17:20:00 "equipment fault" "SouthEast" 14-Jul-2002 21:32:00 90.83 60133 14-Jul-2002 23:53:00 "thunder storm" ⋮
You can access table variables by using dot notation, referring to a table variable by name. With dot notation, you can treat table variables like arrays.
Plot the power loss against outage time. To access these variables from the table, use dot notation.
Calculate the durations of the power outages and plot them against
OutageTime. To calculate the durations, subtract
RestorationTime. The result,
OutageDuration, is a
duration array, because arithmetic with
datetime values produces lengths of time as output. Some of these outage durations are long, so change the format of the y-axis tick values from hours to years by using
ytickformat. The fact that some outages apparently last for years indicates there might be a few questionable data values in the file. Depending on how you plan to analyze the data, you can either reprocess it in some way or remove the rows containing bad values.
OutageDuration = T.RestorationTime - T.OutageTime; plot(T.OutageTime,OutageDuration) ytickformat("y")