How to perform a for loop over a single excel column

I'm trying to change the color my scatter plot points depending on a 3rd column with a for loop that would iterate over the column. Here is my code:

data=xlsread('datafile.xlsx');
x = data(:,2);
y = data(:,3);
z = data(:,4);
for k = drange(length(z))
    if z(k) == -2
        c = [1,0,0];
        sz = 100;
    else
        c = [0,1,0];
        sz = 10;
    end
end
scatter(x,y,sz,c, 'filled')

Any help?

[Luna]

Could you please share your datafile.xlsx? What you are expecting from the code?

[Guillaume]

Also what is drange? I'm assuming it's a function otherwise the for k is pointless.

[Maaya]

I can't share data file due to the nature of the data/source project, but it's organized into three columns. The first two columns are coordinates which I would plot, and the third column would change the color of the point (for example, if the value is -3 then the code would make that particular point larger and the color red). The values in the third column are either 1,0, -1,-2,-3. If it doesn't match a value, then the point would stay a smaller size and green.

[Maaya]

drange is probably an error on my part. I'm trying to loop through the length of the 3rd column

Answer 1

[Guillaume]

I don't see the point of a loop. Simply use your 3rd column to construct a Nx3 matrix of colours:

colours = [1, 0, 0        ... -3
           0, 0, 1        ... -2
           0.5 0.5 1      ... -1
           0, 1, 0        ... 0
           0.2 .4 .6];    %   1
sizes = [100               ... -3
         50                ... -2
         20                ... -1
         10                ... 0
         5];               %   1

data = xlsread('datafile.xlsx')
rowindex = data(:, 4) + 4;  %rescale from -3...1 to  1...5. For more generic code, use the 2nd output of ismember
rowsize = sizes(rowindex);
rowcolour = colours(rowindex, :);
scatter(data(:, 2), data(:, 3), rowsize, rowcolour, 'filled');