Split array in 3 groups by using one column values

Hi,

I would like to split my data in 3 groups based on the values in axis 1

x = < 25 i would like to get a 0

x = > 25 < 419 i would like to get a 1

x = > 419 i would like to get a 2

how can I do this?

% Clear memory
clear; close all;
% Load data
T=readtable('SC01001 (2018-11-23)15sec.csv','PreserveVariableNames',true)

x1=T(:,1); %Date
x2=T(:,2); % Time
y1=T(:,3); % Axis 1

if 
    y1 <25 
    y1  = 0
elseif 
        y1 25>y1<419
        y1 = 1
elseif 
    y1 >419
    y1 = 2
 

end

Answer 1

[Marta G]

You shouldnt use a vector in a if condition.

In your case, it would be more effective to use this

loc=find(y1<25);
y(loc)=0;
loc1=find(y1>25 & y1<419);
y(loc1)=1;
loc2=find(y1>419);
y(loc2)=2;

If you are new to matlab you might understand the problem better with a for loop.

for i=0:length(y1)
    if(y1(i)<25)
        y(i)=0;
    elseif (y1(i)>25 & y1(i)<419)
        y(i)=1;
    else
        y(i)=2;
    end
end

I prefer to not rewrite any variable i am using until it is completely necessary.

Make sure you really need those intervals and consider what you have to do if y1=25 since in your original code it would not enter any if else condition

[Ankit]

small correction in the first line of the for loop, i think by mistake you wrote 0 instead of 1.

[Annick]

I tried both of them,

at the first one, while using the location method, I get the following error message:

Undefined operator '<' for input arguments of type 'table'.

Error in main (line 10)

loc=find(y1<25);

but while using the for loop I get the following error message:

Error using main (line 11)

Subscripting into a table using one subscript (as in t(i)) or three or more subscripts (as in t(i,j,k)) is not

supported. Always specify a row subscript and a variable subscript, as in t(rows,vars).

How can I solve this problem?

[Ankit]

could you post the code which throws above error when you are using for loop? What is "t" in your code?

As based on your question, solution provided by Marta G will not throw any error.

[Annick]

This is everything i have

% Clear memory
clear; close all;
% Load data

T=readtable('SC01001 (2018-11-23)15sec.csv','PreserveVariableNames',true)

x1=T(:,1); %Date
x2=T(:,2); % Time
y1=T(:,3); % Axis 1

for i=1:length(y1)
    if(y1(i)<25)
        y(i)=0;
    elseif (y1(i)>25 & y1(i)<419)
        y(i)=1;
    else
        y(i)=2;
    end
end

The error code it gaves is

Error using tabular/length (line 211)

Undefined function 'length' for input arguments of type 'table'. Use the HEIGHT, WIDTH, or SIZE functions

instead.

Error using main (line 12)

Subscripting into a table using one subscript (as in t(i)) or three or more subscripts (as in t(i,j,k)) is not

supported. Always specify a row subscript and a variable subscript, as in t(rows,vars).

for i=1:length(y1)

[Ankit]

I didn't see any error in the above code. Are you able to readtable ? you can see y1 in workspace? you attached xlsx file why not attached csv file? this is how y look when i use your attach excel sheet

[Annick]

Everything above the for loop works for me. This is the screen I get. Even when I try the xlsx file, i keep getting the same error message

[Marta G]

Hello,

Thank you Ankit for your correction

There is a step missing:

x1=T(:,1); %Date
x2=T(:,2); % Time
y1=table2array(T(:,3)); % Axis 1
for i=1:length(y1)
    if(y1(i)<25)
        y(i)=0;
    elseif (y1(i)>25 & y1(i)<419)
        y(i)=1;
    else
        y(i)=2;
    end
end

Make sure in future problems that you read the error and understand what it means, as that line missing is easily solvable. If you need matrix or vectors instead of table you can use table2array: https://es.mathworks.com/matlabcentral/answers/380821-how-to-convert-table-to-matrix