Extracting data from matrix row vector

I have a double Streams with some process I have got vector F which has a value Now I want to go back to the Streams and locate value matching value of F; get 100 columns forward and collect all the data between those two columns. I tried with ismember to locate the position of F in Streams but no success

 Data=Streams(J: (J-2544))%does not work

Answer 1

[Star Strider]

MATLAB by default increments using the colon ‘:’ operator. If you want it to decrement, you have to tell it specifically to use a negative step.

See if this does what you want:

Data=Streams(J : -1 : (J-2544));

Notice the ‘-1’ step.

[Sag]

I got a warning for code X=Streams(J: -1 : (J-2544));

Warning: Integer operands are required for colon operator when used as index

[Star Strider]

Well, -1 is an integer, so it’s not the problem.

What is ‘J’? It must also be an integer, and greater than 2544.

[Sag]

J is very small value 3.4514e-04

[Star Strider]

That is not going to work as you have written it. First, ‘J’ is a floating-point value, and second, it will generate negative indices the way you have written your array reference. Array indices must be integers greater than zero. ‘J’ must be an integer greater than 2544.

[Sag]

Yes I could not get the code running. As a solution, I created another vector 22544 columns before J and named as P. Then I started data analysis 2544 columns after P.

J = min(abs(Time - P(1))) Final=Streams(J: +1 : (J+2544));

[Star Strider]

Is your problem solved now?

[Sag]

Still there is Warning: Integer operands are required for colon operator when used as index for code Final=Streams(J: +1 : (J+2544)); But the data looks okay Just wanted to know that would above warning affect the data analysis.. Thanks!

[Star Strider]

If you cannot address your data arrays correctly, it could affect your data analysis.

‘J’ still needs to be an integer to create your subscript vector.