Find min value of each column of 2D lattice and plot

Hey everyone,

I am looking to create a 10 x 10 lattice with randomly assigned values for each coordinate then find the minimum value of each column of the lattice and finally plotting the lattice with the lowest number of each column coloured to show visually.

so far all I have is this:

clc
clear
P = randi(10, 10, 10);
for i = 1:1:10
    [row(i), column(i)] = min(P(:,i));
    [x,y] = meshgrid(1:10,1:10);
    xlim([1,10])
    ylim([0,10])
    axis equal
    x_l = reshape(x,[],1);
    y_l = reshape(y,[],1);
    figure; scatter(x_l,y_l)
    hold on
    scatter(x_l(row(i)),y_l(column(i)), 'R', 'filled')
end

but as you can tell, it doesn't work.

I hope this makes sense!

Thanks

Answer 1

[Dyuman Joshi]

It is better to define variables not varying with the loop index, out of the loop. Moreso, as you are using figure().

It's not clear to me, if you want to color the minimum value or the index of the minimum value in each column. The code below corresponds to coloring the minimum value of each column.

Edit - Clarification below in the comments to color the index (first occurance) of the minimum value.

n=10;
P = randi(n, n, n)

P = 10×10

4 4 5 10 6 1 8 1 9 5 9 10 6 7 3 10 10 1 4 1 5 10 4 7 6 10 3 7 1 10 1 7 4 1 8 3 3 8 8 10 6 8 1 1 2 1 6 1 10 8 4 1 7 9 10 6 6 9 8 7 7 5 6 4 5 2 4 7 1 4 2 10 9 2 1 6 6 1 7 3 7 2 4 3 4 4 10 1 8 5 10 5 6 10 7 10 2 1 7 5

[x,y] = meshgrid(1:n);
x_l = reshape(x,[],1);
y_l = reshape(y,[],1);
figure; scatter(x_l,y_l)
xlim([1,n])
ylim([0,n])
axis equal
xticks(1:n)

for i = 1:n
    [~,idx] = min(P(:,i));
    hold on
    scatter(i,n+1-idx, 'R', 'filled')
end

You can achieve the result without the loop as well (As Rik mentioned below)

figure
scatter(x_l,y_l)
xlim([1,n])
ylim([0,n])
axis equal
xticks(1:n)
hold on
%directly obtain the indices
[~,ctr]=min(P)

ctr = 1×10

4 6 5 4 8 1 10 1 3 2

scatter(1:n,n+1-ctr,'G','filled')

[Rik]

You can also use this syntax to get all the minval elements without a loop:

minval = min(P,[],1);

If you want to something with the indices, you may need sub2ind to convert back to linear indices.

[James Kosiol]

Thanks for your answers. Yes, I am looking to colour the minimum value in each column. However, I am looking for something like this: with the P matrix you gave in the answer

the resulting plot should look like this

[Dyuman Joshi]

I have edited my answer, please check!

[James Kosiol]

Excellent work! exactly what I was after. Many thanks.

[Dyuman Joshi]

You are Welcome!

Answer 2

[Mathieu NOE]

not sure if I understood really what you want to do

maybe this ?

clc
clear
N = 10;
[x,y] = meshgrid(1:N,1:N);
xlim([1,N])
ylim([0,N])
axis equal
x_l = reshape(x,[],1);
y_l = reshape(y,[],1);
figure(1); scatter(x_l,y_l)

for i = 1:N
    P = randi(N, N);
    [m, ind] = min(P,[],'all','linear');
    [r,c] = ind2sub(size(P),ind);
    hold on
    pause(0.4)
    scatter(r,c, 'R', 'filled')
end

[James Kosiol]

Thanks for your answer, but it is not what I am looking for. Very close though, please see my pictures in the prior comments.