I currently have a cell array consisting of 7x1 vectors. I need to extract the first element (1,1) of each vector from each cell and store these values in a new array. This is what I currently have:
for j = 1:numel(xvalues)
cellj = xvalues{j};
a = cellj(1:1);
avalues(1:j) = a;
end
However, I am just generating a cell array with the first element of the last cell, repeating.
How can I fix this?
You can also use cellfun to apply a function to each element in a cell array. So to extract the first element of each vector the following should work.
avalues = cellfun(#(x) x(1),xvalues);
Cellfun loops through each element in the cell array and passes it in to the anonymous function via #(x). We then process x by taking the first element x(1).
In cases such as yours, where the cell contents are matrices of the same size, and assuming your inputs are small enough (meaning that neither memory nor runtime are imminent issues) you can convert the cell array into a numeric matrix and select a vector along the relevant dimension:
function out = q48740494
%% Generate some data:
c = squeeze(num2cell(randi(20,7,1,20),[1,2]));
% c = 20×1 cell array of {7x1 double}
%% Convert this into a numeric array and output:
out = cell2mat(c.'); out = out(1,:);
% BONUS: another version of the line above.
% out = subsref(cell2mat(c.'), substruct('()', {1,1:numel(c)}) ) ;
Related
I have a column matrix and a cell array which has two columns.The first column has 1x2 doubles and the second column has 1x1 doubles.
For example
columnMatrix = [1;5];
cellArray = {[1,8],[10];[8,1],[20];[4,6],[80];[3,5],[40];[14,16],[85];[5,10],[36]};
I would like to search each element of columnMatrix in cellArray(:,1) and then return its corresponding value in cellArray(:,2)
For example the output has to be like this
newCell = {[1],[10,20];[5],[40,36]};
I tried using the ismember function in this way
[~,idx] = ismember(cell2mat(cellArray(:,1)),columnMatrix (: , 1));
This returns all the indices which have the searched element but they are in two seperate columns and I can not perform any other logical operation to get the corresponding second column entry.
Is there some way this operation can be achieved? Could some one please help?
Thanks
First of all, convert first column of cellArray to a matrix so it would be easier to search values in. Then iterate over columnMatrix values (e.g. using arrayfun, but you could also use for loop), find rows that match (any across columns) and select corresponding values from the second column of cellArray, converting to numeric array ([cellArray{...,2}]). Finally, append the columnMatrix as the first column of the resulting cell array:
columnMatrix = [1;5]; cellArray = {[1,8],[10];[8,1],[20];[4,6],[80];[3,5],[40];[14,16],[85];[5,10],[36]};
mat = cell2mat(cellArray(:,1));
values = arrayfun(#(x) [cellArray{any(mat==x,2),2}], columnMatrix, 'uni', false);
result = [num2cell(columnMatrix), values];
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)
Let's say I have array A(n,k) and vector b(1,4). Matrix and vector's context are on Galois Field (2).
Is there any way to convolute each row of A with vector b without for loop?
For example if A is of size (4,5) then the command should do the following:
conv(A(1,:),b)
conv(A(2,:),b)
conv(A(3,:),b)
conv(A(4,:),b)
Any ideas?
You can first convert A to a cell array and then use cellfun to apply your function to every element of the cell array, such as:
cellA = num2cell(A, 2) % creates a cell array where each element is a row of A
result = cellfun(#(row)(conv(row, b)), cellA);
Here #(row)(conv(row, b)) is an anonymous function that takes one element of the cell array and applies your conv function to it and your b vector
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 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 =