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arraysmatlabmatrix
Kristada673
Kristada673

Reputation: 3744

How to extract rows of a matrix based on conditions that apply to different columns at once?

For example, say I have a 3-column matrix of news notifications, where the first column gives the serial number of news read in a sequence, the second column givess the Category of the news, and the third column gives whether the notification was opened or not (binary, 1 for read or 0 for not read). So, an excerpt might look like this:

1    12     1
2    13     0
3    13     1
4    12     0
5    14     1
6    13     0
7    12     0
8    13     1
9    14     0
10   12     1

And I want all the rows where notifications from category 12 were read. So, the output should be this:

1    12     1
10   12     1

So, if the data matrix is called input, and the resultant matrix I want is named output, I would write the following code:

for i=1:size(input,1)
    temp = input(input(:,2)==12,:);
    output = temp(temp(:,3)==1,:);
end

But I suppose this should a trivial thing to do in MATLAB. So, is there a one liner that does this?

Upvotes: 2

Views: 70

Answers (2)

Robert Seifert
Robert Seifert

Reputation: 25232

Here is a solution using the supposed to be fast in-built function ismember, which is actually the dedicated function for what you want to achieve:

%// data
A =[1    12     1
    2    13     0
    3    13     1
    4    12     0
    5    14     1
    6    13     0
    7    12     0
    8    13     1
    9    14     0
    10   12     1]

%// sequence to search for
x = [ 12 1 ]

%// filtering
out = A( ismember(A(:,2:3),x,'rows'), : )

out =

     1    12     1
    10    12     1

Upvotes: 0

AVK
AVK

Reputation: 2149

output=input(find(input(:,2)==12 & input(:,3)==1),:)

Upvotes: 4

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