Indexing for a double in cell array matlab - matlab

I have a cell array called Event of 179X59 entries and each element is a <1X14> double
so for example Event{1,1} is a 14 bit binary number in it.. like 0 1 0 0 0 0 0 0 0 0 1 0 0 0 which is spread out through columns 1 to 14 so each columns has a bit.
Now my task is to index through each element of the cell array and get into the double and assign a particular alphabet say a for the first bit if I see 1.
So if my alphabets are A through N for a binary 1 1 1 1 1 1 1 1 1 1 1 1 1 1, need to get
A B C D E F G H I J K L M N instead of that binary number.
So for the example give in the second line 0 1 0 0 0 0 0 0 0 0 1 0 0 0 I need to get
0 B 0 0 0 0 0 0 0 0 K 0 0 0
and in the end should return B,K removing zeros.
I have tried assigning each element to a matrix and tried using strrep but its not helping me out.

Without removing zeros:
alphabet = [11:24]; %// numbers. Replace values as needed
resultzeros = bsxfun(#times, alphabet, vertcat(Event{:}));
resultzeros = reshape(mat2cell(resultzeros, ones(1, size(resultzeros,1))), size(Event));
If you then need to remove zeros:
result = cellfun(#(x) nonzeros(x).', resultzeros, 'uni', 0);
Or directly:
result = cellfun(#(x) alphabet(x~=0), Event, 'uni', 0);
Example:
>> Event = {[0 0 1 0], [1 1 1 1]; [1 1 0 0], [0 0 1 1]};
>> alphabet = [4 5 6 7];
gives
result{1,1} =
6
result{2,1} =
4 5
result{1,2} =
4 5 6 7
result{2,2} =
6 7

Code
cellfun(#(x) cellstr(char(nonzeros(x.*[65:65+numel(x)-1])))', Event,'uni',0)
Results
For a sample Event:
Event = {
[0 1 0 1 0 0 1] [0 1 0 1 0];
[0 1 1 1 0] [0 0 0 1 1 1 0 0 0 0 1 1 0 1]}
Output -
>> Event{:}
ans =
0 1 0 1 0 0 1
ans =
0 1 1 1 0
ans =
0 1 0 1 0
ans =
0 0 0 1 1 1
>> out{:}
ans =
'B' 'D' 'G'
ans =
'B' 'C' 'D'
ans =
'B' 'D'
ans =
'D' 'E' 'F'
Of course, the number of columns and rows in Event at its "upper level" are maintained with out -
>> Event
Event =
[1x7 double] [1x5 double]
[1x5 double] [1x14 double]
>> out
out =
{1x3 cell} {1x2 cell}
{1x3 cell} {1x6 cell}

I suppose that time is not critical, so you can at least loop. Rough sketch:
alphabet = {A, B, C, D, E...}
j= 0;
for i=1:nBit
if( Event{1,1}(i) == 1)
EventAlphabet{1,1}{j} = alpabet{i};
j = j + 1;
end
end
Your question is a little bit unclear, so my answer is a rough sketch that may help you nontheless.

Related

How to leave only the elements that appear once per specific row x column per page?

I have a 3D array. I need to remove any elements that are in the same row, column position but on the next page (3rd dimension), and only use the first occurrence at that position. So if all pages were to multiply the result would be 0.
Since the 3D array may be of any size, I can't hard code solutions like isMember. I also can't use unique because elements can be the same, just not share the same position.
For example, input:
A(:,:,1) = [ 1 0 2];
A(:,:,2) = [ 1 1 0];
A(:,:,3) = [ 0 1 0];
the desired output is:
A(:,:,1) = [ 1 0 2];
A(:,:,2) = [ 0 1 0];
A(:,:,3) = [ 0 0 0];
How can I accomplish this?
Not the most elegant, but at least it works.
A(:,:,1) = [ 1 0 2 ];
A(:,:,2) = [ 1 1 0 ];
A(:,:,3) = [ 0 1 0 ];
for ii = 1:size(A,1)
for jj = 1:size(A,2)
unique_el = unique(A(ii, jj, :)); % Grab unique elements
for kk = 1:numel(unique_el)
idx = find(A(ii,jj,:) == kk); % Contains indices of unique elements
if numel(idx) > 1 % If an element occurs more than once
A(ii, jj, idx(2:end)) = 0; % Set to 0
end
end
end
end
A
A(:,:,1) =
1 0 2
A(:,:,2) =
0 1 0
A(:,:,3) =
0 0 0
I loop over the first two dimensions of A (rows and columns), find any unique elements which occur on a certain row and column location through the third dimensions (pages). Then set all occurrences of a unique element after the first to 0.
Given a more elaborate 3D matrix this still works:
A(:,:,1) = [1 0 2 0; 2 1 3 0];
A(:,:,2) = [1 1 0 0; 2 2 1 0];
A(:,:,3) = [0 1 1 3; 1 2 2 4];
A(:,:,1) =
1 0 2 0
2 1 3 0
A(:,:,2) =
0 1 0 0
0 2 1 0
A(:,:,3) =
0 0 1 3
1 0 2 4
If you want the first non-zero element and discard any element occurring afterwards, simply get rid of the unique() call:
A(:,:,1) = [1 0 2 0; 2 1 3 0];
A(:,:,2) = [1 1 0 0; 2 2 1 0];
A(:,:,3) = [0 1 1 3; 1 2 2 4];
for ii = 1:size(A,1)
for jj = 1:size(A,2)
idx = find(A(ii,jj,:) ~= 0); % Contains indices of nonzero elements
if numel(idx) > 1 % If more than one element
A(ii, jj, idx(2:end)) = 0; % Set rest to 0
end
end
end
A(:,:,1) =
1 0 2 0
2 1 3 0
A(:,:,2) =
0 1 0 0
0 0 0 0
A(:,:,3) =
0 0 0 3
0 0 0 4
My solution assumes, that, for a given "position", EVERY value after the first occurence of any value is cleared. Some of the MATLAB regulars around here had some discussions on that, from there comes the "extended" example as also used in Adriaan's answer.
I use permute and reshape to rearrange the input, so that we have all "positions" as "page" columns in a 2D array. Then, we can use arrayfun to find the proper indices of the first occurence of a non-zero value (kudos to LuisMendo's answer here). Using this approach again, we find all indices to be set to 0.
Let's have a look at the following code:
A(:,:,1) = [1 0 2 0; 2 1 3 0];
A(:,:,2) = [1 1 0 0; 2 2 1 0];
A(:,:,3) = [0 1 1 3; 1 2 2 4]
[m, n, o] = size(A);
B = reshape(permute(A, [3 1 2]), o, m*n);
idx = arrayfun(#(x) find(B(:, x), 1, 'first'), 1:size(B, 2));
idx = arrayfun(#(x) find(B(idx(x)+1:end, x)) + idx(x) + 3*(x-1), 1:size(B, 2), 'UniformOutput', false);
idx = vertcat(idx{:});
B(idx) = 0;
B = permute(reshape(B, o, m , n), [2, 3, 1])
Definitely, it makes sense to have a look at the intermediate outputs to understand the functioning of my approach. (Of course, some lines can be combined, but I wanted to keep a certain degree of readability.)
And, here's the output:
A =
ans(:,:,1) =
1 0 2 0
2 1 3 0
ans(:,:,2) =
1 1 0 0
2 2 1 0
ans(:,:,3) =
0 1 1 3
1 2 2 4
B =
ans(:,:,1) =
1 0 2 0
2 1 3 0
ans(:,:,2) =
0 1 0 0
0 0 0 0
ans(:,:,3) =
0 0 0 3
0 0 0 4
As you can see, it's identical to Adriaan's second version.
Hope that helps!
A vectorized solution. You can use the second output of max to find the index of the first occurence of a nonzero value along the third dimension and then use sub2ind to convert that to linear index.
A(:,:,1) = [ 1 0 2];
A(:,:,2) = [ 1 1 0];
A(:,:,3) = [ 0 1 0];
[~, mi] =max(logical(A) ,[], 3);
sz=size(A) ;
[x, y] =ndgrid(1:sz(1),1:sz(2));
idx=sub2ind( sz, x,y,mi);
result=zeros(sz) ;
result(idx) =A(idx);

Perform "outer product" of 2-D matrix and return a 3-D array in MATLAB

I would like to do an operation on a 2-D matrix which somehow looks like the outer product of a vector. I already have written some codes for this task, but it is pretty slow, so I would like to know if there is anything I can do to accelerate it.
I would like to show the code I wrote first, followed by an example to illustrate the task I wanted to do.
My code, version row-by-row
function B = outer2D(A)
B = zeros(size(A,1),size(A,2),size(A,2)); %Pre-allocate the output array
for J = 1 : size(A,1)
B(J,:,:) = transpose(A(J,:))*A(J,:); %Perform outer product on each row of A and assign to the J-th layer of B
end
end
Using the matrix A = randn(30000,20) as the input for testing, it spends 0.317 sec.
My code, version page-by-page
function B = outer2D(A)
B = zeros(size(A,1),size(A,2),size(A,2)); %Pre-allocate the output array
for J = 1 : size(A,2)
B(:,:,J) = repmat(A(:,J),1,size(A,2)).*A; %Evaluate B page-by-page
end
end
Using the matrix A = randn(30000,20) as the input for testing, it spends 0.146 sec.
Example 1
A = [3 0; 1 1; 1 0; -1 1; 0 -2]; %A is the input matrix.
B = outer2D(A);
disp(B)
Then I would expect
(:,:,1) =
9 0
1 1
1 0
1 -1
0 0
(:,:,2) =
0 0
1 1
0 0
-1 1
0 4
The first row of B, [9 0; 0 0], is the outer product of [3 0],
i.e. [3; 0]*[3 0] = [9 0; 0 0].
The second row of B, [1 1; 1 1], is the outer product of [1 1],
i.e. [1; 1]*[1 1] = [1 1; 1 1].
The third row of B, [1 0; 0 0], is the outer product of [1 0],
i.e. [1; 0]*[1 0] = [1 0; 0 0].
And the same for the remaining rows.
Example 2
A =
0 -1 -2
0 1 0
-3 0 2
0 0 0
1 0 0
B = outer2D(A)
disp(B)
Then, similar to the example 1, the expected output is
(:,:,1) =
0 0 0
0 0 0
9 0 -6
0 0 0
1 0 0
(:,:,2) =
0 1 2
0 1 0
0 0 0
0 0 0
0 0 0
(:,:,3) =
0 2 4
0 0 0
-6 0 4
0 0 0
0 0 0
Because the real input in my project is like in the size of 30000 × 2000 and this task is to be performed for many times. So the acceleration of this task is quite essential for me.
I am thinking of eliminating the for-loop in the function. May I have some opinions on this problem?
With auto expansion:
function B = outer2D(A)
B=permute(permute(A,[3 1 2]).*A',[2 3 1]);
end
Without auto expansion:
function B = outer2Dold(A)
B=permute(bsxfun(#times,permute(A,[3 1 2]),A'),[2 3 1]);
end
Outer products are not possible in the matlab language.

Check neighbour pixels Matlab

I have a A which is 640x1 cell. where the value of each cell A(i,1) varies from row to row, for example A(1,1) =[], while A(2,1)=[1] and A(3,1)=[1,2,3].
There is another matrix B of size 480x640, where the row_index (i) of vector A corresponds to the col_index of matrix B. While the cell value of each row in vector A corresponds to the row_index in matrix B. For example, A(2,1)=[1] this means col_2 row_1 in matrix B, while A(3,1)=[1,2,3] means col_3 rows 1,2&3 in matrix B.
What I'm trying to do is to for each non-zero value in matrix B that are referenced from vector A, I want to check whether there are at least 4 other neighbors that are also referenced from vector A. The number neighbors of each value are determined by a value N.
For example, this is a part of matrix B where all the zeros"just to clarify, as in fact they may be non-zeros" are the neighbors of pixel X when N=3:
0 0 0 0 0 0 0
0 0 0 0 0 0 0
0 0 0 0 0 0 0
0 0 0 X 0 0 0
0 0 0 0 0 0 0
0 0 0 0 0 0 0
0 0 0 0 0 0 0
As shown, because N=3, all these zeros are pixel X's neighbors. So if more than 4 neighbor pixels are found in vector A then do something e.g G=1 if not then G=0;
So if anyone could please advise. And please let me know if any more clarification is needed.
The first thing I would do is to convert your cell of indices A to a logic matrix Amat. This makes it easier to check how many neighbours are included in A.
Here is a solution that uses this conversion. I hope the comments are enough to make it understandable.
clear all
clc
nCols = 7;
nRows = 6;
N = 3; %// Number of neighbours
M = 4; %// Minimum number of wanted connections
%// Create cell of indices A
A = cell(nCols,1);
A{1} = [];
A{2} = 1;
A{3} = [1 2 3];
A{4} = [2 5];
A{5} = 3;
A{6} = [3 5];
A{7} = [1 4 6];
%// Generate radom data B
%// (There is a 50% probability for each element of B to be zero)
Bmax = 17;
B = (randi(2,nRows,nCols)-1).*(randi(Bmax,nRows,nCols));
%// Convert the cell A to a logic matrix Amat
Amat = zeros(size(B));
for ii = 1:nCols
Amat(A{ii},ii) = 1;
end
A
B
Amat
for ii = 1:nCols
for jj = A{ii}
if B(jj,ii)>0
%// Calculate neighbour indices with a lower bound of 1
%// and an upper bound of nCols or nRows
col_lim_low = max(1,ii-N);
col_lim_high = min(nCols,ii+N);
row_lim_low = max(1,jj-N);
row_lim_high = min(nRows,jj+N);
%// Get the corresponding neighbouring-matrix from Amat
A_neighbours = ...
Amat(row_lim_low:row_lim_high,col_lim_low:col_lim_high);
%// Check the number of neighbours against the wanted number M
if sum(A_neighbours(:)) > 1 + M
%# do something
fprintf('We should do something here at (%d,%d)\n',jj,ii)
end
end
end
end
The following is a printout from one run of the code.
A =
[]
[ 1]
[1x3 double]
[1x2 double]
[ 3]
[1x2 double]
[1x3 double]
B =
1 5 0 0 11 0 16
0 13 13 0 0 0 9
0 0 0 5 0 0 0
3 8 16 16 0 2 12
0 0 5 0 9 9 0
12 13 0 6 0 15 0
Amat =
0 1 1 0 0 0 1
0 0 1 1 0 0 0
0 0 1 0 1 1 0
0 0 0 0 0 0 1
0 0 0 1 0 1 0
0 0 0 0 0 0 1
We should do something here at (1,2)
We should do something here at (2,3)
We should do something here at (5,6)
We should do something here at (4,7)
Since you have a one-to-one correspondence between A and B, there is no need to work on A. B is a logical matrix (0 if not referenced in A, 1 if referenced). You can therefore apply a simple filter2 function counting the number of active neighbors within the 8 closest elements.
Here is the code
B = rand(10,10); %generate binary matrix
h = [1 1 1;1 0 1;1 1 1]; %filter to be applied
filter2(h,B,'same')>=4 & B>0 %apply filter on B, count minimum of 4 neighbors, if only B>1
EDIT
To transform a cell array B into binary presence (0=empty, 1=not empty), use of cellfunis straightforward
B = ~cellfun(#isempty,B);
And see Armo's response to your previous question for how to create B based on A.

Split matrix in MATLAB using predefined numbers of submatrix rows

I have a matrix A
1 1 0 0
0 1 0 0
1 0 0 1
0 0 1 0
0 0 0 0
0 1 1 1
1 1 0 0
1 0 0 0
0 0 0 1
I want this matrix to be split according to user's input say d = [1 2 3].
for i=2:length(d)
d(i) = d(i) + d(i-1); % d = [1 3 6]
end
This gives d = [1 (1+2) (1+2+3)] = d[1 3 6]. There are 9 rows in this matrix, calculate ceil of [(1/6)*9], [(3/6)*9] and [(6/6)*9]. Hence this gives [2 5 9]. First split up is first two rows , 2nd split up is next (5-2=3) 3 rows and third split is (9-5=4) 4 rows.
The output should be like:
The split up is: 1st split up->
1 1 0 0 % first 2 rows in matrix A
0 1 0 0
2nd split up->
1 0 0 1 % next 3 rows
0 0 1 0
0 0 0 0
3rd split up->
0 1 1 1 % next 4 rows
1 1 0 0
1 0 0 0
0 0 0 1
You can use mat2cell with input d = [1 2 3] to store the final splits in separate cell arrays
B = mat2cell(A, d+1, size(A,2));
or, to adapt it to your computation of the split row sizes:
d = [1 2 3];
c = cumsum(d); % [1, 3, 6]
s = ceil(size(A,1)*c/c(end)); % [2, 5, 9]
n = [s(1) diff(s)]; % [2, 3, 4]
B = mat2cell(A, n, size(A,2));
To display the splits you can add a command similar to:
cellfun(#disp, B)

Compare two vectors of unequal lengths to get a logical array

I need to vectorize the following code:
a = [1 2 3 2 3 1];
b = [1 2 3];
for i = 1:length(a)
for j = 1:length(b)
r(i, j) = (a(i) == b(j));
end
end
The output r should be a logical array:
1 0 0
0 1 0
0 0 1
0 1 0
0 0 1
1 0 0
The closest I can get is:
for j = 1:length(b)
r(:, j) = (a == b(j));
end
Iterating through the shorter vector is obviously more efficient as it generates fewer for iterations. The correct solution should have no for-loops whatsoever.
Is this possible in MATLAB/Octave?
Here's a simple solution using bsxfun.
bsxfun(#eq,b,a')
ans =
1 0 0
0 1 0
0 0 1
0 1 0
0 0 1
1 0 0
bsxfun(#eq, a', b)