How to convert 1x24 cell with (dif_val x 3) to Matrix [all_dif_val x 2]

Hello dear community,

I have one Cell{} 1x24 cell. Cell{1,1} have a 24x3 matrix, Cell{1,2} have a 608x3 matrix, ....., Cell{1,24} have a 12x3 matrix.

I need just one matrix with values from Traj{1,i}(:,1) and Traj{1,i}(:,2)

Both values should be together and be sorted by first values (times), example:

Cell{1,1} = 
1 78
3 47
5 40

Cell{1,2} =
7 76
4 24

Result_Matrix_wanted =
[1 78; 3 47; 4 24; 5 40; 7 76]

If I do a plot , it works by:

for u = 1:length(Cell)
hold on;
p5 = plot(Cell{1,u}(:,1),Cell{1,u}(:,2),'b--o','Color','c');
end

But I can't create a matrix with this method. Can you help me please? Thank you in advice!

Answer 1

[Ameer Hamza]

Try this example

C{1,1} = ...
    [1 78
    3 47
    5 40];
C{1,2} = ...
    [7 76
    4 24];

A = vertcat(C{:});
A = A(:,1:2); % only get first two column
A = sortrows(A, 1);

[Nik Rocky]

Hei dude, you are amazing! Thank you so much! (big heart smile)

[Ameer Hamza]

I am glad to be of help.

[Nik Rocky]

Hello, I have another error now.

My Cells have often the same time values. But I have to interpolate the values to separate x -axis. Example:

Traj{1}(1:10,1)
ans =
    0.1858
    0.2323
    0.2788
    0.3253
    0.3718
    0.4183
    0.4648
    0.5114
    0.5579
    0.6044
    
Traj{3}(1:15,1)
ans =
    0.1858
    0.2323
    0.2788
    0.3253
    0.5114
    0.5579
    0.6044
    0.6509
    0.6974
    0.7439
    0.9300
    0.9765
    1.0230
    1.0695
    1.1160

I want to interpolate it with:

    t_ref = 0:0.01:30; %3001 values

of couse of same x-values on different cells, I cant use vertcat - in this case I get:

F0_t(1:10)
ans =
    0.1858
    0.1858
    0.2323
    0.2323
    0.2788
    0.2788
    0.3253
    0.3253
    0.3718
    0.4183

So I want to interpolate directly cells (withou converting to vectors/matrix) and get new y-values with:

for l = 1:length(Traj)
    new_traj = interp1(Traj{l}(:,1),Traj{l}(:,2),t_ref,'cubic','extrap');
end

So I get array with 3001 same values (last value of last cell Traj{1}("last",1). How can I do it right? Thank you!

[Ameer Hamza]

See cellfun(). You can apply your interpolation function to each cell individually.

[Nik Rocky]

Thank you again! Yes, this is that I want - to have interpolated Cell1, Cell2,....Celln

If I look example on MATLAB-Descripion

A = cellfun(func,C1,...,Cn)

and I find example and modified this:

X = {[1,4,8,10],[2,6,8,9]};
Y = {[1,2,6,7],[5,9,7,6]};
t_ref = 0:0.01:30;
fun = @(x,y)interp1(x,y,t_ref,'linear');
C = cellfun(fun,X,Y,'uni',0);

I tryed to start this, but I get NaN inside of C

if I try to tranfer to my code:

for l = 1:length(Traj)
    new_traj = cellfun(@((Traj{l}(:,1)),(Traj{l}(:,2)))interp1((Traj{l}(:,1)),(Traj{1}(:,2)),t_ref));
end

What i do wrong?

[Ameer Hamza]

Why not specify to extrapolation with interp1

fun = @(x,y)interp1(x,y,t_ref,'linear','extrap');

[Nik Rocky]

fun = @(Traj{1}(:,1),Traj{1}(:,2))interp1(Traj{1}(:,1),Traj{1}(:,2),t_ref,'linear',"extrap");
 fun = @(Traj{1}(:,1),Traj{1}(:,2))interp1(Traj{1}(:,1),Traj{1}(:,2),t_ref,'linear',"extrap");
             ↑
Error: Invalid expression. When calling a function or indexing a variable, use parentheses. Otherwise, check for mismatched delimiters.

can I use for x: Traj{1}(:,1) and y: Traj{1}(:,2) ?

[Nik Rocky]

Please, look inside from my Cell

[Nik Rocky]

I make a steps:

x = Traj{1}(:,1);
y = Traj{1}(:,2);
fun = @(x,y)interp1(x,y,t_ref,'linear','extrap');
%%%Okay
C = cellfun(fun,x,y,'uni',0);

Error using cellfun
Input #2 expected to be a cell array, was double instead.

[Ameer Hamza]

Try this

t_ref = 0:0.01:30; %3001 values
fun = @(x,y) interp1(x,y,t_ref,'linear','extrap');
cellfun(@(x) [t_ref.' fun(x(:,1), x(:,2)).'], Traj, 'Uni', 0)

[Nik Rocky]

You are genius, thank you very much!

I used:

x = Traj{1}(:,1);
y = Traj{1}(:,2);
fun = @(x,y) interp1(x,y,t_ref,'linear','extrap');
C = cellfun(@(x) [t_ref.' fun(x(:,1), x(:,2)).'], Traj, 'Uni', 0);

I get for C: 1x24 cell with 1x6002 interpolated double in format t1,t2,t3....tn,y1,y2,y3,,,yn

Now I have to split cells in two variables or make cells with 2x3001 double.

Can you describe me, how did you know how to feel this function - I was not able to read this on cellfun- or interp1-description on MATLAB manual page!

@(x) [t_ref.' fun(x(:,1), x(:,2)).'], Traj,

its looks for me like a magic!

[Ameer Hamza]

Nikita, Are you running exactly these lines of code? Because they should already output each cell of size 3001x2. Also, the function cellfun is used to apply a function to each element of a cell array. It can be considered a compact for-loop. The cellfun line in my code id equivalent to

C = cell(1,numel(Traj));
for i=1:numel(Traj)
    C{i} = [t_ref.' fun(Traj{i}(:,1), Traj{i}(:,2)).'];
end

in my code, I just used an anonymous function to write the same thing. You can define any function you want to use with cellfun.

[Nik Rocky]

Hello dear Ameer,

I'm sorry for late answer! Your code works, I made a mistake to convert:

t_ref = 0:0.01:30;
%t_ref = t_ref'; <---

Now everything works, but still not like I need. I'm sorry, I think my description of problem was not enough to understand what I need!

I create a diagram now, maybe so you can understand:

So, after creating t_ref values (3000 values from 0 to 30sek) i do interpolation of m Motors (up to four).

t_ref = 0:0.01:30;

m1 = interp1(t,v1,t_ref,'pchip','extrap'); 
m2 = interp1(t,v2,t_ref,'pchip','extrap');
m3 = interp1(t,v3,t_ref,'pchip','extrap');
m4 = interp1(t,v4,t_ref,'pchip','extrap');

After that I want to do a same with Traj{n}, but this interpolation has to be done while small range of t_Traj{n} and not the whole t_ref.

Then, I want calculate a True Positive/True Negative/False Positive/False Negative (I think False Negative make no sense because we have a discret values and amount of "holes" depends on from sampling grid).

[Nik Rocky]

I get it!

Traj_interpl = cell(1,numel(Traj));
for i=1:numel(Traj)
    minValue = min(Traj{i}(:,1));
    maxValue = max(Traj{i}(:,1));
    indexesInRange = t_ref > minValue & t_ref < maxValue;
    t_Traj = t_ref(indexesInRange);
    fun = @(x,y) interp1(x,y,t_Traj,'linear','extrap');
    Traj_interpl{i} = [t_Traj.' fun(Traj{i}(:,1), Traj{i}(:,2)).'];
end

hold on
for u = 1:length(Traj_interpl)  
    hold on;
    p6 = plot(Traj_interpl{u}(:,1),Traj_interpl{u}(:,2),'b--o','Color','c');
end