How to use indexing to identify data in data(1, :) from points identifed in data(2,:)?

Hi all,

I have a 2x17205 array (called vas_med_env; attached).

in vas_med_env(2,:) I have identified :

j= [5.8150 6.8350 7.8550 8.850]

Now I want to use j, to ''extract' data in vas_med_env(1,:) , by using indexing

my approach below:

n = length(j)-1;
vas_med_cycle = cell(n,1) ;
for i = 1:n
    vas_med_cycle{i} = (vas_med_env(1, :),(vas_med_env(2, :),j(i):j(i+1))) ;
end

results in

vas_med_cycle{i} = (vas_med_env(1, :),(vas_med_env(2, :),j(i):j(i+1))) ;
↑
Error: Invalid expression. When calling a function or indexing a variable, use parentheses. Otherwise, check
for mismatched delimiters.

Can you help please?

Answer 1

[Walter Roberson]

You have a right-hand side expression of the form

(A, (B, C))

That has no meaning in MATLAB.

MATLAB does not define any way to create "tuples". That expression would not create a tuple in which the first element is A and the second element is a tuple in which the first element is B and the second element is C.

Perhaps you meant

vas_med_cycle{i} = {vas_med_env(1, :), {vas_med_env(2, :),j(i):j(i+1)}} ;

or perhaps you meant

vas_med_cycle{i} = [vas_med_env(1, :), vas_med_env(2, :), j(i):j(i+1)] ;

[Tomaszzz]

Hi @Walter Roberson. Many thanks for the answer and explanation.

What I aim is to produce is a 3x cell with:

cell 1 being: vas_med_env(1, :) between j(1) and j(2)

cell 2 being: vas_med_env(1, :) between j(2) and j(3)

cell 3 being: vas_med_env(1, :) between j(3) and j(4)

with j refering to values in vas_med_env(2, :) ;

neither of the above procudes this, with:

the first line: producing 3x 1 cell including 1x2 cells each including 1x 1705 double

the second line producing 3x 1 cell each including 1x34412 double

[Walter Roberson]

j = vas_med_env(2, :);
idx1 = j(1):j(2);
idx2 = j(2):j(3);
idx3 = j(3):j(4);
vas_med_cycle(:,i) = {vas_med_env(1, idx1); vas_med_env(1, idx2); vas_med_env(1,idx3) };

Where does i come into this?

[Tomaszzz]

This indded does the trick, thanks!

[Walter Roberson]

I wonder if you want something closer to

idx1 = j(1):j(2)-1;
idx2 = j(2):j(3)-1;
idx3 = j(3):j(4);