How to find a value in a list?
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I have a m-by-3 matrix of numbers (as below) and I would like to find a specific number in a row and then find the other numbers in that same row then write these in a seperate matrix. For example I want to look for the numbers connected to the number 4, in row 1 these will be 15 and 12 and in row 15 these will be 12 and 3. I then want a matrix called 4 to contain the values 15, 12 and 3. I do not want any repeats in this new matrix, hence 12 only appears once in the new matrix.
15 4 12
5 7 2
22 23 21
18 11 10
10 8 14
16 12 11
12 3 6
8 7 5
8 5 9
14 8 9
7 1 2
5 13 9
5 2 13
7 6 1
12 4 3
6 Comments
Matt Fig
on 15 Aug 2012
Questions:
Do you want all of the numbers in a row that has the given number in it, or just those connected to it (adjacent neighbors)? Take the number 15 in your given list. Do you want to include both the 4 and the 12 from row 1 or just the 4?
What if we had a row like this:
4 4 6
Would we count 4 as a neighbor to 4 (Andrei's code will not)?
Will the real array you need to work with have numbers only on [1,23] or what range?
Thanks.
Answers (4)
Ilham Hardy
on 15 Aug 2012
Unchecked..
test_val = [15 4 12;5 7 2;22 23 21;18 11 10;10 8 14;16 12 11;12 3 6;8 7 5;8 5 9;14 8 9;7 1 2;5 13 9;5 2 13;7 6 1;12 4 3];
base_num = 4;
[r4 c4] = find(test_val==base_num);
matrx4 = unique(test_val(r4,:));
matrx4(matrx4==base_num)=[];
HTH, IH
0 Comments
Andrei Bobrov
on 15 Aug 2012
Edited: Andrei Bobrov
on 16 Aug 2012
z = [...
15 4 12
5 7 2
22 23 21
18 11 10
10 8 14
16 12 11
12 3 6
8 7 5
8 5 9
14 8 9
7 1 2
5 13 9
5 2 13
7 6 1
12 4 3];
out = setdiff(unique(z(any(z == 4,2),:)),4);
ADD ( EDIT )
c = unique(z);
n = numel(c);
out = cell(1,n);
for j1 = 1:n
out{j1} = unique(z(conv2(+(z==c(j1)),[1 0 1],'same')>0));
end
0 Comments
Jordan
on 15 Aug 2012
4 Comments
Andrei Bobrov
on 16 Aug 2012
Hi Jordan! Please use:
c = unique(z);
n = numel(c);
out = cell(1,n);
for j1 = 1:n
out{j1} = unique(z(conv2(+(z==c(j1)),[1 0 1],'same')>0));
end
Matt Fig
on 16 Aug 2012
For large data sets, this is the fastest I could come up with:
A = ceil(rand(19e4,3)*255); % Large data set on [1 255]
% Begin Code, store results in cell array T.
m = max(A(:));
T = cell(1,m);
for ii = 1:m
T{ii} = A(any(A==ii,2),:);
T{ii} = sort(T{ii}(:).');
T{ii} = T{ii}([~isempty(T{ii}) diff(T{ii})~=0]);
T{ii} = T{ii}(T{ii}~=ii);
end
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