Plot 2D contour of z at (x,y) coordinates

Hi, I have three arrays with same dimension: xc, rc, P, where xc and yc are coordinates, P is pressure value at (xc,rc). Is there anyway to plot P as a 2D contour?

I know some functions like pcolor(), contourf() can do this thing, but they require P to be a matrix, not an array.

I also know scatter() can do similar thing, but I need a contour (see below), not scattered points. I attach my dataset and the color figure with many scattered points. Thanks for any suggestion!

contour figure (what I want)

scatter figure (what I generate using scatter())

load xc.mat
load rc.mat
load P.mat
scatter(xc,rc,10,P);
axis equal tight, caxis(max(abs(caxis))*[-1 1]);
xlabel('xc'); ylabel('rc');
xlim([0 10]); ylim([0 2]);

Answer 1

[Walter Roberson]

See https://www.mathworks.com/matlabcentral/fileexchange/38858-contour-plot-for-scattered-data

Answer 2

[Voss]

load P
load xc
load rc

n_rows = numel(unique(rc));

xcM = reshape(xc,n_rows,[]);
rcM = reshape(rc,n_rows,[]);
PM = reshape(P,n_rows,[]);

contourf(xcM,rcM,PM,'EdgeColor','none')

axis equal tight, caxis(max(abs(caxis))*[-1 1]);
xlabel('xc'); ylabel('rc');
xlim([0 10]); ylim([0 2]);

[Ying Wu]

@Voss Thanks! But my data is not regular like this (39*175), so I cannot form a coordinate matrix.

[Voss]

@Ying Wu: Hmm, it seems regular:

load P
load xc
load rc

isequal(rc,repmat(unique(rc),1,175))

ans = logical
   1

isequal(xc,repelem(unique(xc),1,39))

ans = logical
   1

But regardless, you can use a scatteredInterpolant (which should give the same result in this case, and should work properly if you do have irregular data):

xcd = double(xc);
rcd = double(rc);

I = scatteredInterpolant(xcd(:),rcd(:),P(:));

[xcM,rcM] = ndgrid(unique(xcd),unique(rcd));

contourf(xcM,rcM,I(xcM,rcM),'EdgeColor','none')

axis equal tight, caxis(max(abs(caxis))*[-1 1]);
xlabel('xc'); ylabel('rc');
xlim([0 10]); ylim([0 2]);