Color background between two ylines patch (datetime)

I have a plot with heartrate over time, using a datetime function. In addition I have two ylines (y=60 and y=100). Now I want to color the area (background) between those y-lines, for my whole timeline using datetime. The function patch does not work, as it cannot deal with datetime functions. How can I do this?

[Geoff Hayes]

Lieke - can you provide a screen shot of what you have and what you want coloured in? I don't understand how the datetime function is an issue since you just want to color the area between those y-lines. Aren't the y-lines just y=60 and y=100?

Answer 1

[Star Strider]

The error is:

Error using patch
Non-numeric data is not supported in 'patch'

So you can’t use it with datetime objects.

If you want a single vertical line, just use plot:

datetime1=datetime('18-Aug-2017 22:56:00');
datetime2=datetime('18-Aug-2017 23:56:00');

figure
plot([datetime1 datetime1],[50 100],'red')
ylim([40 150])
set(gca, 'XTickLabelRotation',45)

Experiment to get the result you want.

[Lieke Numan]

Thanks! But I want to color the whole space between those two lines, instead of only using colored lines. Does anyone know another function that does work within a datetime plot?

[Star Strider]

My pleasure!

If you want to use patch, you can’t use datetime objects.

The fill (link) function works with datetime objects:

datetime1=datetime('18-Aug-2017 22:56:00');
datetime2=datetime('18-Aug-2017 23:56:00');

figure
fill([datetime1 datetime2 datetime2 datetime1],[50 50 100 100],'red')
ylim([40 150])
set(gca, 'XTickLabelRotation',45)

Experiment to get the result you want.

[Lieke Numan]

Thanks a lot! That works perfectly.

Do you also know how I can use transparent colors for the filled area?

[Star Strider]

My pleasure!

You can vary the transparency iwth the 'FaceAlpha' property:

fill([datetime1 datetime2 datetime2 datetime1],[50 50 100 100],'red', 'FaceAlpha',0.5)

See the documentation section on Transparency (link) for details.

The interesting aspect of all this is that fill creates a patch object, and it works with datetime objects by design.

From the documentation:

‘fill(X,Y,C) creates filled polygons from the data in X and Y with vertex color specified by C. ... The values in X and Y can be numeric, datetime, duration, or categorical values.’

[Lieke Numan]

That works perfectly, thanks!

[Star Strider]

My pleasure.

If my Answer helped solve your problem, please Accept it!

Answer 2

[Lieke Numan]

I want to color the space between y=60 and y=100

datetime1=18-Aug-2017 22:56:00

datetime2=18-Aug-2017 23:56:00

This is what I wanted to do:

patch([datetime1 datetime2 datetime2 datetime1],[50 50 100 100],'red')

It also doesn't work when I use datenum(datetime1) within the patch function.