I have a cell array (2 x 6) called "output", each cell in row #1 {1 -> 6, 2} contains a 1024 x 1024 x 100 matrix. I want to apply movmedian to each cell in row #1. I would like to apply this function in dimension = 3 with window size = 5.
output = cellfun(#movmedian(5,3), output,'uniform', 0);
This is the code that I have come up with so far, however, it produces an "unbalenced or unexpected parenthesis or bracket" error. I am unsure what is causing this error. I am also somewhat unsure how to instruct matlab to perform this operation only on row 1 of the cell array, please help!
Thank you for your time!!
The function handle passed as the first argument to cellfun will be sequentially passed the contents of each cell (i.e. each 3-D matrix). Since you need to also pass the additional parameters needed by movmedian, you should create an anonymous function like so:
#(m) movmedian(m, 5, 3)
Where the input argument m is the 3-D matrix. If you want to apply this to the first row of output, you just have to index the cell array like so:
output(1, :)
This will return a cell array containing the first row of output, with : indicating "all columns". You can use the same index in the assignment if you'd like to store the modified matrices back in the same cells of output.
Putting it all together, here's the solution:
output(1, :) = cellfun(#(m) movmedian(m, 5, 3), output(1, :),...
'UniformOutput', false);
...and a little trick to avoid having to specify 'UniformOutput', false is to encapsulate the results of the anonymous function in a cell array:
output(1, :) = cellfun(#(m) {movmedian(m, 5, 3)}, output(1, :));
Related
I get a cell array which contains 103 cells of different dimensions. Each cell of my cell array represents a matrix and it can be displayed as an image. How can I extract each cell (ie each matrix) in a for loop?
I know how to do that one by one but not for the whole cell :
image1 = cellArray{1}; % extract matrix 1 (on 103) from the cell array #1
image2 = cellArray{2}; % and so on
Thanks for your help
The easiest way to loop through your cell array and apply to same function to every cell is to use cellfun. If your function returns a scalar e.g.
f = #(x)max(:)
then it's as simple as
cellfun(f, cellArray)
Note that f above is an anonymous function (or rather a function handle to an anonymous function), but more likely your function will be in its own m-file in which case you need to use the # operator:
cellfun(#f, cellArray)
Lastly, if your output is not a scalar then call
cellfun(#f, cellArray, 'uni' 0)
How can I check whether an element is in a nested cell array?
ex:
A = {{4 5 6};{6 7 8}};
b = 5;
The function
ismember(b,A{1})
does not work.
Is there any solution better than for-loop?
Because each element is a cell, you don't have a choice but to use cellfun combined with ismember, which is the same as using a loop in any case. Your cells are specifically two-deep (per Andrew Janke). Each cell element in your cell array is another cell array of individual elements, so there is no vectorized solution that can help you out of this.
Assuming that each cell is just a 1-D cell array of individual elements, you would thus do:
A = {{4 5 6};{6 7 8}};
b = 5;
out = cellfun(#(x) ismember(b, cell2mat(x)), A);
Which gives us:
out =
1
0
This checks to see if the value b is in each of the nested cell arrays. If it is your intention to simply check for its existence over the entire nested cell array, use any on the output, and so:
out = any(cellfun(#(x) ismember(b, cell2mat(x)), A));
Because each cell element is a cell array of individual elements, I converted these to a numerical vector by cell2mat before invoking ismember.
I have a cell array (A) with size of 400 x 1 and each cell of this array includes a matrix with size 9 x 4. As such, it looks like this:
A={[9x4 double];[9x4 double];...;[9x4 double]};
Now, I want to remove the zero rows from these sub matrices and then obtain a new A cell array called A_new where its sub matrices don't have any zero rows like this:
A_new={[5x4 double];[7x4 double];...;[4x4 double]};
By my below code, I can find the index of rows which are not zero but I couldn't create my cell array like I mentioned above. This is my written code and for the bold part, I have a problem and I couldn't solve it.
for i=1:A_Length
[row,col]=find(A{i,1});
out=[row col];
NNZ_row=unique(row);
Length_NNZ= length(NNZ_row);
for j=1:Length_NNZ
**A_NonZero{i,1}= ??????????**
end
end
What I would do is take each cell, then use all on the opposite of the matrix over all of the columns in each row to determine which rows contain all zeroes. Once you do this, use these locations and remove those rows from this matrix and save this to your new matrix.
As such, do this:
A_new = cell(1,numel(A));
for i=1:numel(A)
mat = A{i};
ind = all(~mat, 2);
A_new{i} = mat(~ind,:);
end
The first line of code creates a new cell array that is the same size as A. Next, for each element in A, extract the matrix at each cell location, use all on the opposite of this matrix to find those elements that we need to keep, then save this new matrix into the corresponding location in A_new.
If you want to do this in a single line of code, use cellfun:
A_new = cellfun(#(x) x(~all(~x,2),:), A, 'uni', 0);
The first argument to cellfun is an anonymous function that performs what the for loop was doing. We find those rows that contain all zeroes and use those to remove the rows in each matrix in the cell array. The second argument is the matrix we want to operate on, which is A. The 'uni' and 0 flags are important because the outputs are not single values but matrices, and so the output of this function will be a cell array that is the same size as A where each element is the matrix for those corresponding locations in A with the zero rows removed.
You should use a combination of cellfun and any:
A_new = cellfun(#(x) x(any(x~=0,2),:), A, 'UniformOutput', false);
should do the trick.
I'm starting to develop a project which uses multi-dimensional arrays very often.
my arrays are mostly 2 , 3 dimensional or so.
As a 2D array sample consider 'A', I may have 2 or more 1D arrays in a cell.
sth like
A=[1, [78,9] [10,65], 9;
2 , 3 , 6;
7 , [9,1] , [91,41,96][10,-1]]
As you saw in 'A(1,2)' there are two 1D arrays.
I don't know which structure I should use to achieve such thing.
moreover I want to be able to have access to all those 1D arrays.
please share your knowledge with me.
try using cell or struct i would recommend cell.
E.g. preinitialize A1:
A1=cell(3,3)
(that would be a 3x3 cell array/matrix). Then you can adress elements with curly brackets ({}). E.g.:
A1{1,1}= 1;
A1(1,1)={1};
both work. You can also define many cells in one line. E.g:
A1(2,:) = {2,3,6};
For the cases with multiarray entries use another cell structure:
B= {[78,9], [10,65]};
A1(1,2) = {B};
and so on. Pay attention to use curly brackets around B (or the coordinate in A1)! Otherwise he would try to merge the cells from B in A1 but that won't do any good because B is a 1x2 cell and you want to give it as argument to one cell in A1.
If you want to return the value inside a cell you have to use curly brackets again:
A1{1,1}
would return 1.
It depends on what you want to do with such a structure. You could use cell arrays for each 1d array entry, and create a matrix of such cell arrays:
a = {1, 2};
b = {-1, 4, 6};
M = [a b];
Alternatively, you can define a sparse 3d array.
I am a beginner at using Matlab and came across cell arrays but I am not sure how to use indexing for it.
I have created a cell array of 5 rows and 3 cols by doing the following:
A = cell(5,3);
Now is it possible to go through the cell array by row first and then col like how a nested for loop for a normal array?
for i=1:5
for j=1:3
A{i,j} = {"random"} //random numbers/ string etc
end
end
With cell arrays you have two methods of indexing namely parenthesis (i.e. (...)) and braces (i.e. {...}).
Lets create a cell array to use for examples:
A = {3, 9, 'a';
'B', [2,4], 0};
Indexing using paranthesis returns a portion of the cell array AS A CELL ARRAY. For example
A(:,3)
returns a 2-by-1 cell array
ans =
'a'
0
Indexing using braces return the CONTENTS of that cell, for example
A{1,3}
returns a single character
ans =
a
You can use parenthesis to return a single cell as well but it will still be a cell. You can also use braces to return multiple cells but these return as comma separated lists, which is a bit more advanced.
When assigning to a cell, very similar concepts apply. If you're assigning using parenthesis, then you must assign a cell matrix of the appropriate size:
A(:,1) = {1,1}
if you assign a single value using parenthesis, then you must put it in a cell (i.e. A(1) = 2 will give you an error, so you must do A(1) = {2}). So it's better to use braces as then you are directly affecting the contents of the cell. So it is correct to go
A{1} = 2
this is equivalent to A(1) = {2}. Note that A{1} = {2}, which is what you've done, will not give a error but what is does is nests a cell within your cell which is unlikely what you were after.
Lastly, if you have an matrix inside one of your cells, then Matlab allows you to index directly into that matrix like so:
A{2,2}(1)
ans =
3
for example:
for i=1:5
for j=1:3
A{i,j} = rand(3)
end
end
should work perfectly fine
just skip the { } on the right side of the =