Saving Data In A For Loop Into An Array

This seems like a basic question, but I can't seem to figure it out.

I have data for multiple spirals and I want all the x,y and z co-ordinates for each spiral in seperate arrays. I cannot preallocate because I am not aware of the size before running the code.

Would really appreciate any help on how to save my co-ordinates for each spiral in seperate arrays. The code is pasted below

clc; clear; close all

spirals = (1:10:61);
dy = max(spirals);
indent = linspace(-255+dy, 255-dy,4);
num = 1:1:7;
cla
hold on
layerheight = [1 2 4 5];
for columns=1:4
    for rows = 1:length(spirals)
        
        center = -250 + (spirals(rows))*num(rows);
        gap=layerheight(columns);
        d=layerheight(columns);
        r = spirals(rows);
        z=(linspace(0,d,10000));
        t=(40*pi/gap)*z;
        x=round(r*cos(t)+center);
        y=round(r*sin(t)+ indent(columns));
        
        plot3(x,y,z,'o','MarkerSize',2)
        %         for counter = 1:length(z)
        %             rowdata(counter) = [x(rows) y(rows) z(counter)];  %this is how I thought of saving the data, but it doesn't work
        %         end
    end
end
hold off
xlim([-255 255])
ylim([-255 255])
zlim([0 5])
grid on
xlabel('\it Increasing Radius \rightarrow')
ylabel('\it Increasing Layer Height \leftarrow')

Answer 1

[Star Strider]

The easiest way would probably be to save them all in separate cell arrays, here ‘xc’, ‘yc’, and ‘zc’:

for columns=1:4
    for rows = 1:length(spirals)
        
        center = -250 + (spirals(rows))*num(rows);
        gap=layerheight(columns);
        d=layerheight(columns);
        r = spirals(rows);
        z=(linspace(0,d,10000));
        t=(40*pi/gap)*z;
        x=round(r*cos(t)+center);
        y=round(r*sin(t)+ indent(columns));
        
        plot3(x,y,z,'o','MarkerSize',2)
        %         for counter = 1:length(z)
        %             rowdata(counter) = [x(rows) y(rows) z(counter)];  %this is how I thought of saving the data, but it doesn't work
        %         end
        xc{rows,columns} = x;
        yc{rows,columns} = y;
        zc{rows,columns} = z;
    end
end

Experiment to get the result you want.

[Hans123]

wow that works perfectly! The purpose is to export the co-ordinates into a text file, but now that I have them in cells I could do it.

Thanks as always, Star Strider!

[Star Strider]

As always, my pleasure!

[Hans123]

Hi StarStrider, just a follow-up on my issue. As I said, I am trying to save the X, Y and Z coordinates into a text file as 3 columns. I am trying to use the writefile command, but I am getting the error message. Undefined function or variable 'writecell'.

I would appreciate if you could tell me what is going on, and how I can write the data in a text file

[Star Strider]

I cannot find any reference to a ‘writefile’ function. The writecell function was introduced in R2019a.

I am not certain how you want to write them. Note that each cell array has 28 elements, each of which is a (1x10000) vector.

Each circle would be described as a (3x10000) matrix. It might be easiest to save each circle ‘X’, ‘Y’, and ‘Z’ vector to a separate sheet of a spreadsheet file (such as Excel), although saving them as their transposes (so a (10000x3) matrix for each) would likely be easier. That will significantly reduce any problems you may have in importing them again. Use the xlswrite function for that. This could easily be programmed in a loop, using the sprintf function to create the matrices for each circle, and the command strings for xlswrite.

[Hans123]

StarStrider! My apologies for getting back to you this late. I figure out the answer and I forgot that I reached out for you for help!

Again I am really sorry.

Thanks for your help, I always appreciate it!

[Star Strider]

No worries!

As always, my pleasure!