I have a for loop and each value a{i} b{i} c{i} is equal each time with a specific number. So I was wondering how can I put all those value in an array through loop. The way that I am using I mean this one [a{i};b{i};c{i}] it seems that it doesn't work! If I keep 2 out of three values is working but I want the data from all of the values (a b c)
You can see the (pseudo)code below:
for i=1:number of cells
Cell{i}.Tri=[a{i};b{i};c{i}]
end
cell2mat is what you need:
a = num2cell(rand(1,10));
b = num2cell(rand(1,10));
c = num2cell(rand(1,10));
abc = cell2mat([a;b;c]);
This can be done without a for loop by using cellfun combined with the cat function. EDIT: As noted in the comments, cellfun is itself a loop.
% Create all variables
a{1}=rand(10);
a=repmat(a,10,1);
b=a;
c=a;
% Add a cell array of equal size to a. The contents of each cell are the dimension along which to concatenate.
catarg=num2cell(ones(size(a)))
% Do the concatenation
d=cellfun(#cat,catarg,a,b,c,'UniformOutput',false);
Related
Is there a way to create an array of sets in Matlab.
Eg: I have:
a = ones(10,1);
b = zeros(10,1);
I need c such that c = [(1,0); (1,0); ...], i.e. each set in c has first element from a and 2nd element from b with the corresponding index.
Also is there some way I can check if an unknown set (x,y) is in c.
Can you all please help me out? I am a Matlab noob. Thanks!
There are not sets in your understanding in MATLAB (I assume that you are thinking of tuples on Python...) But there are cells in MATLAB. That is a data type that can store pretty much anything (you may think of pointers if you are familiar with the concept). It is indicated by using { }.
Knowing this, you could come up with a cell of arrays and check them using cellfun
% create a cell of numeric arrays
C = {[1,0],[0,2],[99,-1]}
% check which input is equal to the array [1,0]
lg = cellfun(#(x)isequal(x,[1,0]),C)
Note that you access the address of a cell with () and the content of a cell with {}. [] always indicate arrays of something. We come to this in a moment.
OK, this was the part that you asked for; now there is a bonus:
That you use the term set makes me feel that they always have the same size. So why not create an array of arrays (or better an array of vectors, which is a matrix) and check this matrix column-wise?
% array of vectors (there is a way with less brackets but this way is clearer):
M = [[1;0],[0;2],[99;-1]]
% check at which column (direction ",1") all rows are equal to the proposed vector:
lg = all(M == [0;2],1)
This way is a bit clearer, better in terms of memory and faster.
Note that both variables lg are arrays of logicals. You can use them directly to index the original variable, i.e. M(:,lg) and C{lg} returns the set that you are looking for.
If you would like to get logical value regarding if p is in C, maybe you can try the code below
any(sum((C-p).^2,2)==0)
or
any(all(C-p==0,2))
Example
C = [1,2;
3,-1;
1,1;
-2,5];
p1 = [1,2];
p2 = [1,-2];
>> any(sum((C-p1).^2,2)==0) # indicating p1 is in C
ans = 1
>> any(sum((C-p2).^2,2)==0) # indicating p2 is not in C
ans = 0
>> any(all(C-p1==0,2))
ans = 1
>> any(all(C-p2==0,2))
ans = 0
I have a big cell array A=cell(a,b,c,d) and a row vector B with dimensions 1-by-b.
I want to build a loop in MATLAB that does the following:
for i=1:n
B = Calculate_row(input1,input2) %this is a function that creates my B row
A{a,:,c,i} = B(:)
end
anyway if I try to do A{a,:,c} = B(:) I receive the following error:
Expected one output from a curly brace or dot indexing expression, but there were b results.
And if I try to do A(a,:,c) = B(:) I receive the following error:
Conversion to cell from double is not possible.
Is there a way to do this? (I know a less elegant way that probably works would be to assign each value to the cell separately, but I would prefer not to do it).
One way to do this is to make B a cell array and then take advantage of comma-separated-lists:
B_cell = num2cell(B);
[A{a,:,c}] = B_cell{:} %// or [A{a,:,c,i}] = B_cell{:} if tim's comment is correct
Have a look at Loren Shure's article Deal or No Deal and also this answer for more.
The problem with your syntax, A{a,:,c} = B(:), is that the RHS (i.e. B(:)) is just one single matrix whereas the LHS is a comma-separated-list of b results. So you are basically requesting that 1 output be assigned to b variables and MATLAB doesn't like that, also hence the error message.
The problem with A(a,:,c) = B(:) is that indexing a cell array with () returns a cell array and you can't just assign a matrix (i.e. B(:)) to a cell array hence you second error.
I have several arrays that are calculated example a,b and c (there are more than three) are calculated: Please note this is just an example the numbers are much larger and are not so basic
a=[1,2,3,4,5] b=[10,20,30,40,50] c=[100,200,300,400,500] and I want a for loop that inserts zeros into it so I can have the new_abc array steps look like.
1st for loop step new_abc=[0,0,0,0,0,0,0,0,0,0,0,0,0,0,0]
2nd for loop step new_abc=[1,0,0,2,0,0,3,0,0,4,0,0,5,0,0]
3rd for loop step new_abc=[1,10,0,2,20,0,3,30,0,4,40,0,5,50,0]
4th for loop step new_abc=[1,10,100,2,20,200,3,30,300,4,40,400,5,50,500]
how can I do this with a for loop?
I started with the code below which gives me the zeros
a=[1,2,3,4,5]
new_abc=zeros(1,length(a)*(3));
But I'm not sure how to place the values of the array a b and c using a for loopinto the correct locations ofnew_abc
I know I could place all the arrays into one large array and do a reshape but the calculated arrays I use become to large and I run out of ram, so reading / calculating each array and inserting them into one common array new_abcusing a for loop works best.
I'm running octave 3.8.1 which is like matlab.
This should do it. You can put a,b,c into a cell array. (you can also put them in a matrix...)
new_abc = zeros(1, 3*numel(a));
in = {a, b, c};
for k = 1:3
new_abc(k:3:end) = in{k};
end
I'd like to replace a specific number of elements of my cell to zero without using for. For example to replace elements of row 2 in example cell a below: How should I proceed possibly using cellfun?
a=cell(2,3);
cellfun(#(x)(zeros(a{x}(2,:))),a);
It gives the error "Bad cell reference operation".
what if I'd like to make row 2 empty again?
Thanks in advance for any help
The action you want to perform requires an assignment within a function. The only way to achieve this is using eval, which is considered bad practice.
A loop is therefore the best remaining option, if you want to keep everything in one script:
A = {randn(2,3),randn(2,3)};
for ii = 1:numel(A)
A{ii}(2,:) = 0;
end
If you don't bother using multiple files, you can put the assignment in a function:
function [ out ] = setZero( cellarray, rowidx )
out = cellarray;
out(rowidx,:) = 0;
end
and use it as follows:
A = cellfun(#(x) setZero(x,2),A ,'uni',0)
You need to find a transformation that turns a given matrix A to a matrix where the second row is all-zero. Here are three alternatives
A=cellfun(#(x) [x(1,:); zeros(size(x(2,:))); x(3:end,:)], A, 'uni', 0)
and
A=cellfun(#(x) diag(1:size(x,1)~=2)*x, A, 'uni', 0)
and
A=cellfun(#(x) bsxfun(#times, (1:size(x,1))' ~= 2, x), A, 'uni', 0)
The first one is the most robust one because it will handle the cases that your matrix has NaN elements. The second and third alternatives simply multiply the second row by zero. The second achieves this by multiplying it with a diagonal matrix where all diagonal elements are 1 except element (2,2) which is zero. The third alternative achieves this using bsxfun.
This is to demonstrate that you can achieve this without for loops however a simple for loop is much more readable.
This is my first time posting so i hope you can help me. I am trying to write a function in matlab.
I have laded data from a file into a cell array. First column contains statements and the second contains T for true og F for false. I now want to split this array into a cell array with the statements and a logical vector with 1 for True and -1 for false.
I use the fgetl within a loop to read all the lines into the cellarray
Try to write it a bit more neatly next time, and consider including a small example.
Here is what you seem to be looking for:
Suppose you have a matrix M and want to split that into M_true and M_false
M = {1,'T';
22,'F';
333,'T'}
idx_T=strcmp(M(:,2),'T')
M_true = M(idx_T,1)
M_false = M(~idx_T,1)