Matrix visualisation with coloured box and numbers

Hello,

I wonder if someone can please help me. I am trying to visualizes a NxM matrix by plotting each matrix entry as a colored square (box). The entry value itself should also be displayed. (Similar to a sudoku grid but with each number value being depicted by a colour as well).

Matrix = [1,2,3;4,3,2;1;4;2]
Matrix =

     1     2     3
     4     3     2
     1     4     2

Thus I would like to plot this matrix as shown above.

Any help much appriciated. Thanks

Answer 1

[Matt Tearle]

imagesc and text. If it's like sudoku in that the range of values is fixed, use image and a custom colormap.

EDIT TO ADD: I realized that it's a bit more involved than I made it sound, so here's an example that makes it all pretty:

n = 4;
m = 5;
Amax = 7;

cmap = autumn(Amax);
A = randi(Amax,m,n);

figure
image(A)
colormap(cmap)
set(gca,'XTick',[],'YTick',[],'YDir','normal')

[x,y] = meshgrid(1:n,1:m);
text(x(:),y(:),num2str(A(:)),'HorizontalAlignment','center')

Answer 2

[Paulo Silva]

Following Matts answer here's one simple example

M=[1,2,3;4,3,2;1,4,2]
imagesc(M)
for a=1:3
    for b=1:3
        text(b,a,num2str(M(a,b)))
    end
end

[Jennifer]

Brilliant thank you!

One slight hiccup with my code is that it now my matrix is inverted -any quick way to solve this? Having a mental block this morning.....

Thanks

[Paulo Silva]

I don't know what's inverted but here's a way to reverse it all, change the code so it fits your needs

clf

M=[1,2,3;4,3,2;1,4,2]

imagesc(M)

for a=1:3

for b=1:3

text(b,a,num2str(M(a,b)))

end

end

set(gca,'XTick',[],'YTick',[]) %stolen code from Matt example :)

set(gca,'XDir','reverse') %reverse X axis

set(gca,'YDir','reverse') %reverse Y axis

[Matt Tearle]

You're probably referring to the y-axis being flipped. So, either

set(gca,'YDir','normal')

or

axis xy

[Matt Tearle]

BTW, I don't know if you want the colors to be fixed to the values, or whether you want the full range of colors to be used every time (regardless of value). Paulo's example uses the full color range (by using imagesc); mine uses a fixed color palette. Hence, with Paulo's example, 1 is dark blue, 4 is dark red; however, if you change M to ones(3), the whole image will be green. That is, 1 = dark blue is not absolute, it's relative. In my example, there are Amax fixed colors, so 3 is always the third color in the palette. That's better if you want the colors to symbolize a fixed value, but Paulo's is better if you want flexibility. It depends whether your matrix has a fixed set of values or not.

[Uros]

First I just wanna say thanks for these answers it's been very helpful, thanks everyone.

And can someone explain me these line of code:

set(gca,'XTick',[],'YTick',[],'YDir','normal')

Thanks

[Paulo Silva]

XTicks and YTicks are those numbers that appear usually below and on the left side of the axes, that code removes them, the YDir is the direction of the increment, close to the origin is the lowest value with the normal option, the reverse option makes the biggest value close to the origin of the axes.

You can have a better explanation at http://www.mathworks.com/help/techdoc/ref/axes_props.html

[Matt Tearle]

To deconstruct the syntax: gca is a function that returns a handle to the current axes. So that line of code sets three properties of the current axes object (Paulo explained what they are very nicely) The x/ytick properties should be set to an array of values; [] is an empty array. Hence, you get no tick marks on the axes.