MATLAB excluding data outside 1 standard deviation

Question

I'm inexperienced with MATLAB, so sorry for the newbie question:

I've got a large vector (905350 elements) storing a whole bunch of data in it. I have the standard deviation and mean, and now I want to cut out all the data points that are above/below one standard deviation from the mean. I just have no clue how. From what I gather I have to make a double loop of some sort?

It's like: mean-std < data i want < mean + std

Answer 1

If the data is in variable A, with the mean stored in meanA and the standard deviation stored in stdA, then the following will extract the data you want while maintaining the original order of the data values:

B = A((A > meanA-stdA) & (A < meanA+stdA));

Here are some helpful documentation links that touch on the concepts used above: logical operators, matrix indexing.

Answer 2

You can simply use the Element-wise logical AND:

m = mean(A);
sd = std(A);
B = A( A>m-sd & A<m+sd );

Also, knowing that: |x|<c iff -c<x<c, you can combine both into one as:

B = A( abs(A-m)<sd );

Answer 3

Taking A as your original vector, and B as the final one:

B = sort(A)
B = B(find(B > mean-std,1,'first'):find(B < mean+std,1,'last'))

Answer 4

y = x(x > mean-std);
y = y(y < mean+std);

should work. See FIND for more details. The FIND command is being used implicitly in the above code.