CODEWITHSUNDEEP
matlab
shawpnik
shawpnik

Reputation: 111

How to count a specific number in MATLAB?

Two columns in an excel file; first column contains year(Y) and the second column contains values(MWS). Second column has three kinds of values: more than zero, zero and -999. I am trying to count:

I have tried the following codes, which give me sum instead of count. 

yy = unique(Y);
ny = max(Y)-min(Y)+1;

X1 = zeros(ny,1);
X2 = zeros(ny,1);
for i = 1:ny
    X1(i) = sum(MWS((Y == yy(i))==0));   
end
for i = 1:ny
    X2(i) = sum(MWS((Y == yy(i))>=0));   
end

Any help would be apprecaited.

Best regards

Upvotes: 2

Views: 93

Answers (2)

JimR
JimR

Reputation: 2225

Something like this, using the inbuilt accumarray would work and avoids needing the loops.

Y = [2013, 2013, 2013, 2014, 2014, 2014, 2015, 2015, 2015];
MWS = [0, 0, 1, 0, 0, 0, 1, 1, 1];

[unique_years, ~, indexes] = unique(Y);
numZerosInYear = [unique_years', accumarray(indexes', MWS, [], @(x) sum(x == 0))];
numAboveZeroInYear = [unique_years', accumarray(indexes', MWS, [], @(x) sum(x > 0))];

If you still want to use loops, your original code is almost correct, however you're just indexing MWS incorrectly. The following should work.

for i = 1:ny
    X1(i) = sum(MWS(Y == yy(i)) == 0);
end
for i = 1:ny
    X2(i) = sum(MWS(Y == yy(i)) >= 0);   
end

Upvotes: 2

Autonomous
Autonomous

Reputation: 9075

I see the following problems in your code at first glance:

yy = unique(Y);
ny = max(Y)-min(Y)+1; %this will not be correct if Y has non-consecutive years.

X1 = zeros(ny,1);
X2 = zeros(ny,1);
for i = 1:ny
    % I do not understand what you trying to do on the following line. 
    % You are creating a logical vector which has wherever Y takes the 
    % value = yy(i), fair enough. However, you test for equality with 0,
    % which places ones wherever Y ~= yy(i). MWS(Y == yy(i))==0) returns
    % all those values (not ones, actual values). Then you sum the 
    % values. Hence you are not getting the count, but getting a sum.
    X1(i) = sum(MWS((Y == yy(i))==0));   
end
for i = 1:ny
    % I think you can figure this out now. One mistake here is that you 
    % test for >=0 but you state that you want values greater than zero.
    % I have corrected that in my code.
    X2(i) = sum(MWS((Y == yy(i))>=0));   
end

Lets fix the code now by tweaking your logic. I haven't tested the following, but it should work.

yy = unique(Y);
ny=numel(yy);
X1 = zeros(ny,1);
X2 = zeros(ny,1);

for i = 1:numel(yy)
    X1(i) = sum(MWS(Y==y(i))==0) %how many zeros in year y(i)
    X2(i) = sum(MWS(Y==y(i))>0) %how many > than zero in year y(i)
end

Upvotes: 1

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