I have the index value from a plot. Now what?

Hello,

I have created a plot, any plot will work. Then went in with data cursor function within the plot, right clicked and exported the cursor data. The cursor info, produced a 'DataIndex' value. Say I want the plot to start at the provided index value, how would I go about that?

I am also attempting to create a beginning and end function as I have to use this time interval multiple times.

Example:

Beginning= ____ %the index value, this is where I am not sure how to use the indexed value

End = max(time) %the end of the plot

TimeInterval = (Beginning:End)

plot(load(TimeInterval),deflection(TimeInterval))

Thank you,

Cory

Answer 1

[Walter Roberson]

plot(load(TimeInterval),deflection(Beginning:end))

That is, use the same indexing of your y data as you used for your x data. You were attempting to use your x values to index your y values, instead of using the positions to index each of them.

[Cory Powell]

Perfect. I thought it might be something as easy as that.

Thank you Walter!

[Cory Powell]

Walter,

If I understand correctly I have to apply to same time interval for both the x-axis and they y-axis? So if I were to have load v deflection curve, it should read:

plot(load(timeinterval),deflection(timeinterval))

Does this seem right?

Answer 2

[dpb]

If you plotted with

plot(x,y)

then

x(cursor_info.DataIndex)

is the x value at that index point (which is also the same as

cursor_info.Position(1)

without the need to index into the array.

To set the axes limits at this value for the beginning without changing the upper limit from its existing,

xl=xlim(gca);  % retrieve x-axis current limits
xl(1)=cursor_info.Position(1);  % update lower limit
xlim(gca,xl)                        % and update the axes limits to match

The question on the end depends on whether you want the "prettified" rounded value of the axis upper limit or the (possibly not even at all) value that's the last point in the dataset.

The former is simply xl(2) just obtained, the latter is x(end).

Use whatever is your x-axis variable in place of the placeholder x I used here, of course.

That's all there is to it; nothing exotic. Note that xlim works on actual data values, not the index itself.

[Cory Powell]

Thank you dpb,

For further understanding, what if I use 'clear all' in the code. How would it carry over if I call out the cursor_info.Position(1)?

Cory

[dpb]

Almost no need ever in code for it but if you use it, it'll wipe everything you save prior to that point including the value you just retrieved if it comes after.