Trimming data with for loop

I am trying to write a code that will use a specific column of data to start filling a new array when m(iii)>1, however, it now only gives back the data in the new array when m(iii)>1 so i'm not sure how to fix it. I also want it to collect 720000 data points starting when that first m(iii)>1. Any help would be appreciated, thank you.

length = 720000;

m = acq2.data(:,4);

empty_array2 = zeros(size(length));

for iii = 1:length

if m(iii) > 1

empty_array2(iii) = acq2.data(iii);

end

if iii <= length

end

end

[Gatech AE]

Be careful naming variables after built-in functions. The "length" function returns the largest dimension of an input. Also, you have size(length) where length is defined as a scalar, so your empty_array2 variable is actually only 1 by 1 in size.

Answer 1

[Star Strider]

I am not certain what you want to do.

Try this —

acq2.data = randi([0 5], 10, 5)                         % Create Matrix

acq2 = struct with fields:
    data: [10×5 double]

idx = acq2.data(:,4) > 1                                % Select Rows

idx = 10×1 logical array
   1
   1
   1
   0
   1
   1
   0
   1
   0
   1

empty_array = acq2.data(idx,:)                          % Assign Selected Rows To 'empty_array'

empty_array = 7×5

3 2 3 2 2 2 5 2 3 0 0 4 2 4 3 3 3 4 5 4 4 2 3 4 5 0 2 5 4 2 3 0 1 5 5

This will create ‘empty_array’ with rows of ‘acq2.data’ with values in column 4 are greater than 1. It is probably easier (and more efficient) than the loop.

.

[Sydney Kehoe]

What I want to do is start collecting data from a certain row (iii) from column 4 of a data set when m(iii)>1 happens for the first time. I only want this to happen once because when it does happen for the first time I want that to be the starting data point and then from there I want 720000 points to be collected from the data set. So ideally I would have a new array that has data starting from row iii of column 4 and then ending at that row iii+720000 if that makes any sense at all?

[Star Strider]

I am not certain that I ujnderstand what you want to do.

If you want to collect every row after the first time column 4 is greater than 1, something like this would work:

acq2.data = randi([0 5], 10, 5)                         % Create Matrix

acq2 = struct with fields:
    data: [10×5 double]

Show = acq2.data

Show = 10×5

3 5 1 1 0 1 4 4 4 2 4 5 0 0 1 1 1 5 1 0 3 4 3 5 1 0 0 3 5 5 2 1 5 0 3 2 1 4 1 0 1 2 4 5 5 5 3 2 4 0

start = find(acq2.data(:,4)>1,1,'first')

start = 2

empty_array = acq2.data(start:end,:)

empty_array = 9×5

1 4 4 4 2 4 5 0 0 1 1 1 5 1 0 3 4 3 5 1 0 0 3 5 5 2 1 5 0 3 2 1 4 1 0 1 2 4 5 5 5 3 2 4 0

.

[Sydney Kehoe]

n = 720000;

m = acq2.data(:,4);

empty_array2 = [];

for iii = 1:839272

if m(iii) > 1

empty_array2(iii) = m(iii);

end

if iii <= 839272

end

end

I basically was hoping to put a new column of data into an empty matrix. I want to start to collect this data when m(iii) first is greater than 1. However, this happens more than once so I am not sure how to do it so that I start this new data set when m(iii)>1 for the first time and continues to collect the data through the end of the set. If this doesn't help thank you for your help regardless.

[Star Strider]

I’m sorry, however I am now completely confused.

I have no idea what you want to do.

If you can clarify it, ideally with an example, I will see what I can do.

[Sydney Kehoe]

I just worked out a while loop which I think makes more sense but I am going to attempt to do another post since it is a very different format

[Star Strider]

Great!

Please supply as many details in your new post as you can. A sample of the data you want to process would be important, as well as an example of the result you want.