How to select specific cells rows in a column

So i currently have an array that is similar to this on a much larger scale:

1 1 1 1 1 1 1 1

0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0

1 1 1 1 1 1 1 1

1 1 1 1 1 1 1 1

0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0

I need to write a code that picks out all of the zeros in colum 5 ( the ones that are bolded) but I need it to ignore any subseuent zeros after that (the two rows after)

any help would be great

Answer 1

[per isakson]

%%
M = [
    1 1 1 1 1 1 1 1 
    0 0 0 0 0 0 0 0
    0 0 0 0 0 0 0 0
    0 0 0 0 0 0 0 0
    1 1 1 1 1 1 1 1 
    1 1 1 1 1 1 1 1 
    0 0 0 0 0 0 0 0
    0 0 0 0 0 0 0 0
    ];
%%
isZero  = M(:,5)==0;
%   position of first zero
ixb = find( isZero, 1, 'first' );
%   position of last zero in first sequence of zeros
ixe = find( not(isZero(ixb:end)), 1, 'first' ) + ixb - 2;
%%
z5  = reshape( M(ixb:ixe,5), 1,[] ) 

returns

z5 =
     0     0     0

[Louis Cook]

Sorry didnt know to re ask in here :)

So i tried the above option into my code but it wasnt really working so I guess its easier to put my entire code into this and hopefully there is an easier solution :)

1.csv is an example of a file in which there is only one group of 0's so there is no problem

10.csv is an example of where this is two groups of 0's which is causing a problem

thanks for the help

g=9.81; %acceleration due to gravity
num = 1:78;
ext = ".csv";
JumpData = num + ext;


for f=1:length(JumpData );
inputdata=xlsread(JumpData{f});%extract all data from first jump%
idx = find(inputdata(6:3000,5)==0);%finds all the zeros in the z collumn%
zeroMatrix = inputdata(idx,5);%Turns it into a matrix%
oneMatrix=zeroMatrix+1;%adds to to all the zeros%
t=sum(oneMatrix)/100;%sum all of the zeros and turn into miliseconds%


MH(f)=0.5*g*(0.5*(t^2));
MHFinal=MH';
end

Answer 2

[Cris LaPierre]

I'm a fan of readtable, so although it takes more setup, I think overall it handles tables better.

Here is code that just finds the first set of zeros. I'll let you add the rest of your code to it.

for f=1:length(JumpData)
    % Set import options to capture information in headerlines
    opts = detectImportOptions(JumpData{f});
    opts.VariableDescriptionsLine = 3;
    opts.VariableNamesLine = 4;
    opts.VariableUnitsLine = 5;
    opts.DataLines = 6;
    
    % load data into a table
    data = readtable(JumpData{f},opts,'ReadVariableNames',true);
    
    % find first grouping of zeros in Fz
    idx = find(data.Fz == 0);
    step = find(diff(idx)>1,1)+1;
    idx(step:end)=[];
    % convert length of zeros to time aloft (each 0 corresponds to 0.01 seconds?)
    tm(f) = length(idx)*0.01;
end

[Cris LaPierre]

EDIT: Changing your answer to a comment

Answer by Louis Cook on 6 Jan 2019 at 11:55

Hello thankyou for your response,

the code works near enough perfect :) the only problem is that the output (tm(f)) is coming out a 1x2 matrix and i dont see why as it is only asking for the length of idx.

[Cris LaPierre]

How many files were in JumpData? I'm guessing 2? The code I wrote will make tm a 1xf vector, where f is the number of files in JumpData.

I naively assumed you would want to capture the time for each file. The variable f is your loop counter, so tm(1) is the time in JumpData{1}, tm(2) is the file in JumpData{2}, etc.

If that is not the case, you will need to modify the code I shared to fit your use case.

You can learn more about indexing here.