I'm trying to create a map that has two-element cell arrays as values. Map expects that keys and values have the same number of elements. This code packs those cell arrays into cells in a loop, but I'm suspecting that it can be simplified somehow. Example code:
cells1={'foo1';'foo2';'foo3'};
cells2={'bar1';'bar2';'bar3'};
cells3={'baz1';'baz2';'baz3'};
values=cell(size(cells1));
for ii=1:size(cells1,1)
values{ii}={{cells2{ii},cells3{ii}}};
end
keys=cells1;
containers.Map(keys,values);
you can use vector concatenation and num2cell with 2nd dimension argument (twice if you want to obtain identical result):
% your code
cells1={'foo1';'foo2';'foo3'};
cells2={'bar1';'bar2';'bar3'};
cells3={'baz1';'baz2';'baz3'};
values=cell(size(cells1));
for ii=1:size(cells1,1)
values{ii}={{cells2{ii},cells3{ii}}};
end
% simplified
c = num2cell(num2cell([cells2,cells3],2),2);
% you can also do c = num2cell([cells2,cells3],2); which isn't identical but may be suficcient
isequal(c,values) % yes
Related
Suppose I have a 3x1 cell array called subj that has the following elements:
cell 1: 300x20 double
cell 2: 300x15 double
cell 3: 300X18 double
I want to remove the last quarter rows from every element in each cell as follows:
subj{1}(length(subj{1})*0.25+1:end,:) = []
subj{2}(length(subj{2})*0.25+1:end,:) = []
subj{3}(length(subj{3})*0.25+1:end,:) = []
However I want to be do this in one line and can't figure out a way to do this in Matlab. I messed around with converting the cell array to a matrix, but since there different numbers of columns, it makes it slightly more complicated. Is there a vectorized way to do this in one line? I will be applying machine learning algorithms to each element of subj and it would be great to have this be vectorized for later parts of my code.
Better not assigning empty arrays to a matrix (actually that doesn't work) but reassign the matrix itself:
% loop over the cell array
for i = 1:length(subj)
% determine the index/number of rows. Don't forget to round as MATLAB requires integers for slicing!
idx = round( length(subj{i})*0.25 );
% get the new matrix
NewMat = subj{i}(1:idx,:);
% assign new matrix to the old address, i.e. the content of the cell
subj{i} = NewMat;
end
MATLAB allocates contiguous memory for matrices, so cropping it shouldn't cause much overhead. In particular not as it uses "lazy copying" and; therefore, only copies the matrix when you change any of its values.
I'd like to use fprintf to show code execution progress in the command window.
I've got a N x 1 array of structures, let's call it myStructure. Each element has the fields name and data. I'd like to print the name side by side with the number of data points, like such:
name1 number1
name2 number2
name3 number3
name4 number4
...
I can use repmat N times along with fprintf. The problem with that is that all the numbers have to come in between the names in a cell array C.
fprintf(repmat('%s\t%d',N,1),C{:})
I can use cellfun to get the names and number of datapoints.
names = {myStucture.name};
numpoints = cellfun(#numel,{myStructure.data});
However I'm not sure how to get this into a cell array with alternating elements for C to make the fprintf work.
Is there a way to do this? Is there a better way to get fprintf to behave as I desire?
You're very close. What I would do is change your cellfun call so that the output is a cell array instead of a numeric array. Use the 'UniformOutput' flag and set this to 0 or false.
When you're done, make a new cell array where both the name cell array and the size cell array are stacked on top of each other. You can then call fprintf once.
% Save the names in a cell array
A = {myStructure.name};
% Save the sizes in another cell array
B = cellfun(#numel, {myStructure.data}, 'UniformOutput', 0);
% Create a master cell array where the first row are the names
% and the second row are the sizes
out = [A; B];
% Print out the elements side-by-side
fprintf('%s\t%d\n', out{:});
The trick with the third line of code is that when you unroll the cell array using {:}, this creates a comma-separated list unrolled in column-major format, and so doing out{:} actually gives you:
A{1}, B{1}, A{2}, B{2}, ..., A{n}, B{n}
... which provides the interleaving you need. Therefore, providing this order into fprintf coincides with the format specifiers that are specified and thus gives you what you need. That's why it's important to stack the cell arrays so that each column gives the information you need.
Minor Note
Of course one should never forget that one of the easiest ways to tackle your problem is to just use a simple for loop. Even though for loops are considered bad practice, their performance has come a long way throughout MATLAB's evolution.
Simply put, just do this:
for ii = 1 : numel(myStructure)
fprintf('%s\t%d\n', myStructure(ii).name, numel(myStructure(ii).data));
end
The above code is arguably more readable in comparison to what we did above with cell arrays. You're accessing the structure directly rather than having to create intermediate variables for the purpose of calling fprintf once.
Example Run
Here's an example of this running. Using the data shown below:
clear myStructure;
myStructure(1).name = 'hello';
myStructure(1).data = rand(5,1);
myStructure(2).name = 'hi';
myStructure(2).data = zeros(3,3);
myStructure(3).name = 'huh';
myStructure(3).data = ones(6,4);
I get the following output after running the printing code:
hello 5
hi 9
huh 24
We can see that the sizes are correct as the first element in the structure is simply a random 5 element vector, the second element is a 3 x 3 = 9 zeroes matrix while the last element is a 6 x 4 = 24 ones matrix.
I am using two cells for storing the targeted and the expected value of a neural network process in matlab. I have used two 1*1 cell array for storing the values respectively. And here is my code.
cinfo=cell(1,2)
cinfo(1,1)=iter(1,10)%value is retrieved from a dataset iter
cinfo(1,2)=iter(1,11)
amp1=cinfo(1,1);
amp2=cinfo(1,2);
if amp1 == amp2
message=sprintf('NOT DETECTED BY THE DISEASE');
uiwait(msgbox(message));
But when i run the above code, the get the following error :
??? Undefined function or method 'eq' for input arguments of type 'cell'.
Error in ==> comparison at line 38
if amp1 == amp2
How to solve this problem?
The problem is how you indexed things. A 1x1 cell array does not make a lot of sense, instead get the actual element in the single cell, by indexing with curly brackets:
amp1=cinfo{1,1}; # get the actual element from the cell array, and not just a
amp2=cinfo{1,2}; # 1x1 cell array by indexing with {}
if (amp1 == amp2)
## etc...
However, note that if amp1 and amp2 are not scalars the above will act weird. Instead, do
if (all (amp1 == amp2))
## etc...
Use isequal. That will work even if the cell's contents have different sizes.
Example:
cinfo=cell(1,2);
cinfo(1,1) = {1:10}; %// store vector of 10 numbers in cell 1
cinfo(1,2) = {1:20}; %// store vector of 20 numbers in cell 2
amp1 = cinfo(1,1); %// single cell containing a length-10 numeric vector
amp2 = cinfo(1,2); %// single cell containing a length-20 numeric vector
if isequal(amp1,amp2)
%// ...
In this example, which parallels your code, amp1 and amp2 are cell arrays consisting of a single cell which contains a numeric vector. Another possibility is to directly store each cell's contents into amp1, amp2, and then compare them:
amp1 = cinfo{1,1}; %// length-10 numeric vector
amp2 = cinfo{1,2}; %// length-20 numeric vector
if isequal(amp1,amp2)
%// ...
Note that even in this case, the comparisons amp1==amp1 or all(amp1==amp2) would give an error, because the vectors have different sizes.
I have a matrix of cells, call it M. The matrix dimensions are n^3.
Each cell contains an array of indices (a result of a regexp query on some string, not that it matters).
I want to intersect the indices in the arrays in each cell of M.
How can I do that? If I use intersection function how does it know to take the indices from inside the arrays in each cell?
As I understand I have to use cells because the inner arrays are of unknown size.
Is this what you want to do?
A = M{1};
for i = 2:numel(M)
A = intersect(A, M{i});
end
I don't think there's a neat way to do this using a single intersect call, or with e.g. cellfun.
If you only want the intersection of specific indices, you can do:
A = indices(1);
for i = indices(2:end)
A = intersect(A, M{i});
end
If I have an array (of unknown length until runtime), is there a way to call a function with each element of the array as a separate parameter?
Like so:
foo = #(varargin) sum(cell2mat(varargin));
bar = [3,4,5];
foo(*bar) == foo(3,4,5)
Context: I have a list of indices to an n-d array, Q. What I want is something like Q(a,b,:), but I only have [a,b]. Since I don't know n, I can't just hard-code the indexing.
There is no operator in MATLAB that will do that. However, if your indices (i.e. bar in your example) were stored in a cell array, then you could do this:
bar = {3,4,5}; %# Cell array instead of standard array
foo(bar{:}); %# Pass the contents of each cell as a separate argument
The {:} creates a comma-separated list from a cell array. That's probably the closest thing you can get to the "operator" form you have in your example, aside from overriding one of the existing operators (illustrated here and here) so that it generates a comma-separated list from a standard array, or creating your own class to store your indices and defining how the existing operators operate for it (neither option for the faint of heart!).
For your specific example of indexing an arbitrary N-D array, you could also compute a linear index from your subscripted indices using the sub2ind function (as detailed here and here), but you might end up doing more work than you would for my comma-separated list solution above. Another alternative is to compute the linear index yourself, which would sidestep converting to a cell array and use only matrix/vector operations. Here's an example:
% Precompute these somewhere:
scale = cumprod(size(Q)).'; %'
scale = [1; scale(1:end-1)];
shift = [0 ones(1, ndims(Q)-1)];
% Then compute a linear index like this:
indices = [3 4 5];
linearIndex = (indices-shift)*scale;
Q(linearIndex) % Equivalent to Q(3,4,5)