Matrix from vectors (dynamic number of columns)

Dear Matlab users I want to create a matrix form vectors V1, V2 and V3 (same number of rows), number of rows equal to number of rows in vectors) but the number of column is dynamic (relative to an integer called Nbr), let explain with an example:

V1 = [1 2 3]
V1 = [4 5 6]
V1 = [7 8 9]
t = [0.1 0.2 0.3] % (used for an future plot)

If Nbr = 1 the matrix came

1
2
3

I plot (t, V1), the legend is Case1

If Nbr = 2 the matrix came

1 4
2 5
3 6

I plot (t, V1, t, V2), the legend is (Case1, Case2)

If Nbr = 3 the matrix came

1 4 7
2 5 8
3 6 9

I plot (t, V1, t, V2, t, V3), the legend is (Case1, Case2, Case3)

I attached the plot for the last case (Nbr = 3)

Answer 1

[Stephen23]

Putting all of your data into separate variables is a really bad idea, so the first thing to do is to save them in one matrix (I called it M). Then your whole task becomes trivial using basic MATLAB indexing, and you can also supply the whole matrix (or part of it) to plot instead of supplying separate input arguments. Much easier!

t = [0.1,0.2,0.3];
M = [1,2,3;4,5,6;7,8,9]; % your data
% create the legend strings:
C = arrayfun(@num2str,1:size(M,1),'uni',0);
C = strcat({'Case '},C);
% pick how many lines to plot:
N = 2;
plot(t,M(1:N,:).')
legend(C(1:N))

See how easy MATLAB can be? It creates this plot:

EDIT: without the legend, to show how the matrix is plotted without wasting time using loops:

t = [0.1,0.2,0.3];
M = [1,2,3;4,5,6;7,8,9];
N = 2;
plot(t,M(1:N,:).')

[Ced]

Just in case his legend generation is confusing to you, this is a mini example with just the bare basics:

t = [0.1,0.2,0.3];
M = [1,2,3;4,5,6;7,8,9]; % your data

% pick how many lines to plot:
N = 2;
for i = 1:N
   plot(t,M(i,:)')
   hold on; % this "keeps" previous lines
end

[Ferial Assmani]

Dear Stephen, thank you for your help, for the matrix, is there a way to ful it dynamically from a vector (nxm elements) to form a matrix n (rows) m (columns), i.e

Vec = [1 2 3 4 5 6]

fixing n = 3 and m = 2, i get a matrix

1 4
2 5
3 6

So the relation of m and n is the length(Vec)

[Stephen23]

@Ced: why do you introduce a loop? This is a total waste of MATLAB's abilities. I showed how the matrix can be simply plotted at once, which also has the advantage that the lines are colored according to the axes' ColorOrder property (i.e. each line gets its own color). By introducing a loop you make all lines have the same color, make the code slower, and use for more code than I used to plot it. I don't see the point.

You claim that it "is a mini example with just the bare basics", but you actually made it more complicated. Compare my solution:

t = [0.1,0.2,0.3];
M = [1,2,3;4,5,6;7,8,9];
N = 2;
plot(t,M(1:N,:).')

[Stephen23]

@Ferial Assmani: You can use reshape:

>> Vec = [1,2,3,4,5,6]
Vec =
     1     2     3     4     5     6
>> M = reshape(Vec,3,2)
M =
     1     4
     2     5
     3     6

[Ced]

@Stephen: Since the OP seems to be new to Matlab, I find that M(1:N,.).' makes it hard to understand what is plotted (rows vs columns). No need to make a fuss about it.

And since R2014b, it is not true anymore that all the colors will be the same.

[Stephen23]

The plot function is well documented: "The plot function plots columns of Y versus columns of X".

"Since the OP seems to be new to Matlab" I am going to show them neat and efficient ways of using MATLAB, so that they can proceed to efficiently handling larger and more complicated tasks. That is what I try to do.

[Ferial Assmani]

Sorry for my bad questions, but the source of my Data is not a open source, so i must adapt my reading to it, i resume my traitement into the following points :

1. i have a number of txt files (number is for loop) in each one, i read a matrix, for each position (number is for loop) i read a matrix (ratio and time);
2. i extract the maximum of ration (his correspondent time) and it position (called interest position)
3. i extract the pair (ratio, time) of all interest position in all case
4. i plot the pair (ratio, time) of all interest position in all case

Source of data

Traitement

Plot

Answer 2

[Azzi Abdelmalek]

v=[1 2 3;4 5 6;7 8 9]
t = [0.1 0.2 0.3] 
n=2
plot(t,v(:,1:n)')
legend(genvarname(repmat({'Case'},1,n),'Case'))

[Ferial Assmani]

Sorry, a read the vector form a txt file (a previous traitement) so i haven't the matrix i ful it from the vector, so i cut some elements to ful rows, next rows, to next

[Ferial Assmani]

Dear Expert: i have tried your guidelines it work except the plot looping:

    clear all; clc; close all;
    %
    V_Time = [1, 2, 3];                           % Time Vector fixe length
    %
    V_Data = 1:1:12;                              % Data Vector
    Nbr_Position = 2;                             % Nbr of position 
    Nbr_Case   = 2;                               % Nbr of cases
    %
    N_Rows= length(V_Time);                       % Nbr of rows for matrix
    N_columns= length(V_Data)/N_Rows;             % Nbr of columns for matrix
    M_Brut= (reshape(V_Data,[N_Rows,N_columns])); % Brut matrix from Data Vector
    %
    % in nexte i trim the Brut matrix to forme the paire (Time, Data) for all
    % case for all poisition
    % -------------------------------------------------------------------------
    %        Position 1        | .. to .. (i Position)
    %--------------------------------------------------------------------------
    % Case1 | .. to .. (j Case)| Case 1 | .. to .. (j Case)
    %--------------------------------------------------------------------------
    % And i plot ( Time Data(case1, ... case(j)) for all position
    %
    for i=1:Nbr_Position                                     % loop by position
           M_Nett{i} = M_Brut(:,(i):(Nbr_Position):(end));   % Nett matrix
              for j=1:Nbr_Case                               % loop by case
                  plot(V_Time,M_Nett{i}(:,1:j)')             % plot pair
                  title(['Graphes for Node ' num2str(i)])    % title
                  legend(genvarname(repmat({'Case'},1,j),'Case'))  % legend
              end
    end
    %
    % Listing Data
    % Brut Data
    %--------------------------------------------------------
    %           Case1            |           Case2          |
    % -------------------------------------------------------
    %  Position 1  |  Position 2 |  Position 1 | Position 2 |
    %--------------------------------------------------------
    %     1       |        4     |     7      |      10     |
    %     2       |        5     |     8      |      11     |
    %     3       |        6     |     9      |      12     |
    %--------------------------------------------------------
    % Nette Data to plot
    %--------------------------------------------------------
    %         Position 1        |         Position 2        |
    % -------------------------------------------------------
    %   Case1     |    Case2    |   Case1    |    Case2     |
    %--------------------------------------------------------
    % Time | Data | Time | Data | Time | Data | Time | Data |
    %--------------------------------------------------------
    %   1  |   1  |  1   |  4   |  1   |  7   |  1   |  10  |
    %   2  |   2  |  2   |  5   |  2   |  8   |  2   |  11  |
    %   3  |   3  |  3   |  6   |  3   |  9   |  3   |  12  |
    %--------------------------------------------------------

Thank