How to add a line to scatter plot

Hello! I created a scatter plot with maximum temperatures and daily data from the 1930s to 2020. I want to create a straight line in the 100F (for high temperature reference) in my y axis but I can't. I tried many codes from Matworks but no success.

Hope anyone can help me with this.

This is the plot I get and the code I used

figure('Name','Daily TMAX');
 hold on
 scatter(Date,DailyTMAX,'b','*')

Answer 1

[Cris LaPierre]

Use yline.

scatter(rand(1,100),rand(1,100),'b','*')
yline(0.7)

[Nuria Andreu]

Thank you!! it worked

Answer 2

[Chunru]

Date = datetime([1930:2020], 1, 1);
DailyTMAX = randn(size(Date));

figure('Name','Daily TMAX');
hold on
scatter(Date,DailyTMAX,'b','*')

yline(max(DailyTMAX), 'r--')

[Nuria Andreu]

Thank you! Both answers worked

[Cris LaPierre]

Just a comment that hold on is not necessary when using xline or yline. However, adding it has no adverse effect.

Also, it is best practice to always pair a hold on with a corresponding hold off.

[Nuria Andreu]

Thank you Cris, I will practice more!