Create a simple table from using data from other table and an Iteration loop

Dear all,

I am very frustrated trying to create a very basic thing in Matlab for the past 4 hours with no success.

i have a table named time = [0;1;2;3;4;5;6;7;8;9;10;12;14;16;18;20;22;25;28;30];

I am trying to make a second table dt that will be the difference of the current minus the previous time.

dt = [1;1;1;1;1;1;1;1;1;1;1;2;2;2;2;2;2;3;2] using the following loop:

for i=2:20
    k=time(i)-time(i-1);
    dt(i-1)= k;
end

but I get the following error:

Subscripting a table using linear indexing (one subscript) or multidimensional indexing (three or more subscripts) is not supported. Use a row

subscript and a variable subscript.

Please help!!!

BR

[Stephen23]

>> time = [0;1;2;3;4;5;6;7;8;9;10;12;14;16;18;20;22;25;28;30];
>> diff(time)
ans =
     1
     1
     1
     1
     1
     1
     1
     1
     1
     1
     2
     2
     2
     2
     2
     2
     3
     3
     2

Answer 1

[Jeff Miller]

If you are really using the table datatype (as the error message suggests), then you are not indexing it properly. A table has variables, and you can index those as you are trying to do. So, I imagine you would need something like

for i=2:20
    k=time.time(i)-time.time(i-1);
    dt(i-1)= k;
end

It is a bit confusing to use 'time' as the name of both a table and a variable within that table, though you can do that if you want.

Looking at your code, though, I wonder why you need to use the table datatype at all. Why not just have a vector for time and a vector for dt?

[Michael Perakis]

ok, and how would I go on doing that?

[Jeff Miller]

Pretty much like you already are doing it, but without the table datatype. For example,

clear all
time = [0;1;2;3;4;5;6;7;8;9;10;12;14;16;18;20;22;25;28;30];
dt = zeros(numel(time)-1,1);
for i=2:20
    k=time(i)-time(i-1);
    dt(i-1)= k;
end

Actually there is also a nice matlab function called 'diff' for successive differences, so you could just use that:

time = [0;1;2;3;4;5;6;7;8;9;10;12;14;16;18;20;22;25;28;30];
dt = diff(time);

[Michael Perakis]

Thank you very much!