how to not plot NaN but still have same array length

I have y = array of 10000 data. A lot of them are NaN. I dont want to plot NaN but if I use plot(y(~isnan(y)),'o'); my plot only goes up to ~1000. It should still go up to 10000 but not plot those with NaN. How can i do this ?

Answer 1

[Star Strider]

The NaN values themselves will not plot. This may produce breaks in the plotted line, so if you don’t want the breaks, your only option is to interpolate.

The easiest way to interpolate is to keep your original independent variable to be your interpolating variable, the eliminate all the NaN values from your dependent variable and the corresponding values of you independent variable, then use interp1.

Example:

x = 1:10;
y = [2 4 2 9 NaN 3 1 NaN 6 10];

xs = x(~isnan(y));
ys = y(~isnan(y));

yi = interp1(xs, ys, x, 'Linear');

figure(1)
subplot(2,1,1)
plot(x, y)
grid
subplot(2,1,2)
plot(x, yi)
grid

[RuiQi]

Sorry for not being specific. I am using a scatter plot. I want data that are NaN to be invisible on the plot. So i dont think i need to interpolate ?

[Star Strider]

The data that are NaN will be invisible on the plot.

MATLAB does not plot NaN values, so you can just use your original data in your scatter plot without any modification.

If you also want to eliminate them from your data, use code similar to what I used to create ‘xs’ and ‘ys’, then plot those.

Answer 2

[Image Analyst]

Your code basically extracts the non-nan elements and plots only those so it won't go all the way up to 1000. You need to plot x also to have it still go up to 1000. See this little demo:

numPoints = 200; % Make 1000 if you want.  I used 200 to make it easier to see what's going on.
% Make sine wave sample data.
x = 1 : numPoints;
period = 200;
y = sin(2 * pi * x / period);
% Introduce 80 nans
nanLocations = randi(length(x), 1, 80);
y(nanLocations) = nan;
% Plot entire array, even the nans, which won't appear.
plot(x, y, 'bo-', 'LineWidth', 2); 
grid on;

% Set up figure properties:
% Enlarge figure to full screen.
set(gcf, 'Units', 'Normalized', 'OuterPosition', [0 0 1 1]);
% Get rid of tool bar and pulldown menus that are along top of figure.
set(gcf, 'Toolbar', 'none', 'Menu', 'none');
% Give a name to the title bar.
set(gcf, 'Name', 'Demo by ImageAnalyst', 'NumberTitle', 'Off')

[atek]

what if y(1:100) = NaN? Matlab begins plotting at first real value, and I want it to plot NaN's as blank spaces

[Walter Roberson]

Use xlim() to force the left boundary to start at 0