Is there a way to get MATLAB to filter out specific rows in arrays?

I’ve been looking for a method to filter out specific rows of data in an array. I’ve got a < 750 x 3 double> array containg car data that looks like this:

10000.5 3 120

10001.0 5 112

10001.5 1 117

10002.0 4 119

10002.5 3 122

10003.0 2 120

10003.5 5 114

10004.0 1 118

10004.5 4 120

Where column 1 is track time, column 2 is the car number, and column 3 is the speed of the car at that specific track time. I’m looking for a method to filter out rows of data based on the car number. For example, if the data in the rows associated with car numbers 3 and 4 are not needed, I’d have a resulting array that looks like this:

10001.0 5 112

10001.5 1 117

10003.0 2 120

10003.5 5 114

10004.0 1 118

Eventhough I haven’t found a specific MATLAB funtion that will do this type of filtering, I would think this can be done in MATLAB. Any ideas are appreciated. Thanks.

Answer 1

[Kelly Kearney]

Take a look at the ismember function:

data = [...
10000.5 3 120
10001.0 5 112
10001.5 1 117
10002.0 4 119
10002.5 3 122
10003.0 2 120
10003.5 5 114
10004.0 1 118
10004.5 4 120]

new = data(~ismember(data(:,2),[3 4]),:)

[Brad]

Kelly, good catch. I forgot all about this function. Thanks.

Answer 2

[Lokesh Ravindranathan]

The following code does filtering for your problem.

a = [10000.5  3  120;
     10001.0  5  112;
     10001.5  1  117;
     10002.0  4  119;
     10002.5  3  122;
     10003.0  2  120;
     10003.5  5  114;
     10004.0  1  118;
     10004.5  4  120];

       list1 = a(:,1,:)
       list2 = a(:,2,:)
       list3 = a(:,3,:)
       keyIndex = (list2~=3) &(list2~=4)
       b = [list1(keyIndex) list2(keyIndex) list3(keyIndex)]

The matrix b returns the matrix of interest. There are other ways of implementing the filtering, but this is the simplest I could think of.