Filtering data from a table. How can I save values that are higher that 0.5?

I can't find a solution to my problem. I have data stored in a table. This data represent the behavior of a signal in time.

I want to create a program that reads each row of a table if a value on a specific column is 0 do not save, but if the value is higher start saving.

Example:

0 0  0  0  0  1 1.2 1.5 1.6 1.3  1 0 0 0 0 0 0 0 0  2 2.4 5 3 2  0 0 0 0 0 0 0 0 0 0  . . . . . . . . . .
---------------        save 1             -------------------      save 2    -------------------------

Code:

b=a(:,4)        %column to search
rate=length(b)  %number of rows
for i=1:rate
  b1 = b(i);    % read value of row
  if b1 < 0.5
  end
  if b1 > 0.5    
  end
end

*I have an overwrite problem

Hope you can help me. Thanks.

[Turlough Hughes]

It would be helpful to attach your variable as ".mat", also are you looking to save all rows of a based on a(:,4)?

[Mariana]

Yes, I want to save all rows with values higher than 0.5 with a different name everytime I find them again.

Answer 1

[Pandiyaraj Gnanasekar]

Hi Mariana Gutierrez,

b = a ( : , 4 ); %column to search

rate = length(b); %number of rows

V = zeros(rate,1);

for i =1:rate

if b(i) > 0.5

V(i) = b(i);

end

end

I think this might help! Try this or explain a bit more in next comment.

[Mariana]

a = xlsread(filename)

b = a ( : , 4 ); %column to search

rate = length(b); %number of rows

V = zeros(rate,1);

for i =1:rate

if b(i) > 0.5

V(i) = b(i);

end

end

*I tried this, but it saves the same values of b. I dont understand why. It suppose to just save values higher than 0.5....

Answer 2

[Turlough Hughes]

You could get an index for each chunk of data as follows:

idx=find(a(:,4)>0.5)
idx2=find((idx(2:end)-idx(1:end-1))~=1);
idx2=unique(sort([min(idx); idx(idx2); idx(idx2+1); max(idx)])); % this is the start and end of each chunk of data.

Then to store data like this you would typically put it into a cell array:

for c=1:length(idx2)/2
    data{c,1}=a(idx2(2*c-1):idx2(2*c),:);
end

EDIT: As per comments below

[Mariana]

I have an error on this line.

idx2=unique(sort([1 idx2 idx2+1 max(idx)])); % this is the start and end of each chunk of data.

Error:

Dimensions of arrays being concatenated are not consistent

[Turlough Hughes]

Ah ok I made a mistake, I think you could just modify this line to include the semi-colons as follows:

idx2=unique(sort([min(idx); idx(idx2); idx(idx2+1); max(idx)]));

Edit; the following should work.

[Mariana]

I tried it , but is not working it also saves 0 values.

[Turlough Hughes]

You could then access the data as follows:

data1=data{1,1}
data2=data{2,1}
%etc.

[Mariana]

Data1 and Data2 have values of 0 and also higher ones. I thinks is not filtering correctly.

This what I am trying:

a = xlsread(filename)

t = a( : , 1) : %time value

b = a ( : , 4 ); %column to search

c = find (b <= 0.5) %row numbers

values_c= a(c,:) %create a new variable with values lower than 0.5

d = find (b <= 0.5) %row numbers

values_d= a(d,:) %create a new variable with values higher than 0.5

rate = length (values_d)

for i =1:rate

j = i + 1:

t1 = values_d(i,1)

t2 = values_d(j,1)

diff = t2 - t1

if diff > 5

stop(i) = values_d(i);

end

end

change = find(stop ~= );

l = length(change)

Basically, what I am doing is to find all zero values save them in a table and in other table save non zero values.

Then from (values_d higuer than 0.5) I read the column 1 which represents the time if the time difference is higher than 5 seconds it is because a series of 0 happened in between. In other words I should cut it and save with different name every time a find a time gap higher than 5.

[Turlough Hughes]

"I tried it , but is not working it also saves 0 values"

I subsequently edited my answer. There was a problem with the indexing but it should be fine now.

Answer 3

[Pandiyaraj Gnanasekar]

Hi Mariana Gutierrez,

If you want only the values greater than 0.5 and not the zeros. You can simply remove those zeros from the vector b.

try this,

b = a ( : , 4 );

b(b==0) = []; % this will remove values equal to zeros from b vector.

Hope it will solve your problem.