How can I assign different colors to each plotted line?

Hi,

I have the following code:

>>x=1-by-3 matrix
>>y=3-by-9 matrix
>>figure
>>cc=hsv(9);
>>plot(x,y,'color',cc);

The objective is to plot 9 lines using 3 points for each line. The code does that. However, I'm unable to assign different color to each line. I get the following error message: "Color value must be a 3 element numeric vector"

What am I doing wrong?

Amit

Answer 1

[dpb]

At the top level of plot can't pass the array; only a single color vector.

Save the line handles and set their properties...

hL=plot(x,y,'k');  % just so see what happens later...
for i=1:length(hL),set(hL(i),'color',cc(i,:));end

NB: must reference the vector of the row of the colormap array.

Seems like should be able to use the vector syntax but set isn't apparently smart enough--

set(hL,{'color'},{cc})

fails as all other perturbations of syntax I can think of do as well. Documentation demonstrates some string cases like 'Tag' property by no numeric ones so is of no help.

ERRATUM

The above presumption against set is wrong; it's bad syntax on my part not clearly interpreting the documentation despite reading it...as the followup sidebar with IA shows, I finally figured out the problem. For posterity, the key is the cell array itself must have the proper dimensions, not the array being held in a cell.

set(hL,{'color'},{cc})  % fails, wrong because size(cc)=[1,1]

Instead use

set(hL,{'color'},mat2cell(cc,length(cc),1))  % success!!

or return the color array (or whatever property in general) as the cell by doing the conversion when creating it--

cc=mat2cell(colormap(9),9,1);
set(hL,{'color'},cc)

where used constants for the sizes to minimize parentheses-nesting.

[Image Analyst]

Amit's "Answer" moved here. Amit, you should also accept and Vote for dpb's solution.

Hi dpb,

Thank you. It worked perfectly!

Amit

[Image Analyst]

You can also not worry about setting the color in each call if you want to take the default color order. My attached code shows how you can change that.

[dpb]

Good point, IA...btw, do you know anything more about the set syntax? Is there any way to write the following and I just couldn't get it quite right or is set just dumber than it should be?

set(hL,{'color'},{cc})

I tried every perturbation I could think of including trying to klew it in by matching rows with things like and similar to

set(hL,cellstr(repmat('color',9,1)),{cc})

I guess one could use arrayfun and avoid the explicit loop or the like but seems like the above should be possible...

[Image Analyst]

You can use set to set multiple different parameters, like 'Color' and 'LineWidth', by passing them in separately, or in cells . But you cannot sort of automatically increment the handles in the same set statement. Here's an illustration:

numberOfElements = 10;
x = 1 : numberOfElements;
numberOfCurves = 8;
y = rand(numberOfElements, numberOfCurves);
hLines = plot(x,y,'k');  % just so see what happens later...
% cm = rand(numberOfCurves, 3); % Random colors.
cm = jet(numberOfCurves); % Predefined "jet" colormap.
for k = 1 : length(hL)
%   set(hLines(i), 'Color', cc(i,:), 'LineWidth', 3);   % Works
  set(hLines(k), {'Color', 'LineWidth'}, {cm(k, :), 3});  % Also works
end
% This will not work to set all hLines objects at once
% to different colors:
set(hLines, {'Color', 'LineWidth'}, {cm, 3});  % Fails

[dpb]

From

doc set
....
set(H,pn,MxN_pv) sets n property values on each of m graphics objects, where m = length(H) and n is equal to the number of property names contained in the cell array pn.  This allows you to set a given group of properties to different values on each object.
...

Oh, wait a minute...there's the rub in that the cell content has to be the value and I put into a single cell instead of a cell array...

Going back to OP's example...

>> cc=colormap(hsv(9));
>> for i=1:length(cc),ccc(i,1)={cc(i,:)};end
>> whos ccc
Name      Size            Bytes  Class    Attributes
ccc       9x1               756  cell               

>> hL=plot(rand(3,9),'k-');
>> set(hL,{'color'},ccc)
>>

Joy ensues!!! Works as should...I had kept using

ccc=mat2cell(cc);

or variations thereon that all still led to size(ccc)=1x1, NOT 9x1 even though content of the cell was length()=9

I'm glad to have finally fingered this out -- I went thru a lot of similar gyrations on the last month's worth of financial records evaluation I did generating a lot of historical views and fixed up a whole series of figures with varying numbers of lines to have consistent coloring across the group. The above would have shortened the code significantly but never figured out where I was making the error until now.

ADDENDUM

So the end result for clarity and succinctness is one can use

cm = mat2cell(jet(nCurves),nCurves,1);
hLines = plot(x,y,'k'); 
set(hLines, {'Color', cm);

I've not tested but I presume one can also use something like your last example above and do multiple properties at one time as well.