Multiply specific parts of cell with cell column

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Ki Loius
Ki Loius 2016-10-24
回答： Ki Loius 2016-10-24
How can I multiply specific parts of a cell array with a cell column?
e.g. y is a 3x5 cell
10 11 12 13 14
15 16 17 18 19
20 21 22 23 24
I want to multiply the y(2:3,2:3) party with y(2:3,5)
16 17 * 19
21 22 24
result should a 2x2 array:
16*19 17*19
21*14 22*14
My attempt did not work:
x = zeros(3,2); %create new empty array (first line should be empty)
for i=2:3
x(i,:)=cell2mat(y(i,2:5)).*cell2mat(y(i,5)));
end

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回答（6 个）

Adam
Adam 2016-10-24
编辑：Adam 2016-10-24
Why do you have a cell array in the first place instead of a numeric array? It is far slower and requires you to use much uglier constructs to do simple maths operations.
y(2:3,2:3) = y(2:3,2:3) .* y(2:3,5);
would work on a numeric array (in R2016b - Andrei Bobrov's alternative is what I always used pre-R2016b)
y = cell2mat( y );
before that will allow you to get away from your cell array.
Andrei Bobrov
Andrei Bobrov 2016-10-24
编辑：Andrei Bobrov 2016-10-24
y1 = {10 11 12 13 14
15 16 17 18 19
20 21 22 23 24};
y = cell2mat(y1);
out = y(2:3,2:3).*y(2:3,5); % R2016b and Octave
out = bsxfun(@times,y(2:3,2:3),y(2:3,5)); % R2016a and before
Alexandra Harkai
Alexandra Harkai 2016-10-24
There could be a typo here:
cell2mat(y(i,2:5))
Probably should be:
cell2mat(y(i,2:3))
So result should be:
16*19 17*19
21*24 22*24
This can be achieved like this, without a loop (see https://uk.mathworks.com/help/matlab/ref/bsxfun.html):
x = zeros(3,2); %create new empty array (first line should be empty)
x(2:3,:) = bsxfun(@times, cell2mat(y(2:3,2:3)), cell2mat(y(2:3,5)));
Ki Loius
Ki Loius 2016-10-24
编辑：Ki Loius 2016-10-24
Thank you for your answers. I just recognized, that I did not provide enough information for my case. The first row and line in my cell are strings. (first two answers do not work)
Answer 3 is not working, since Subscripted assignment dimension mismatch. I have to multiply a NxM part of the matrix with one column
a more precise example would be cell y:
i a b c d e
f 11 12 13 14 15
g 16 17 18 19 20
h 21 22 23 24 25
i 26 27 28 29 30
I want to multiply y(2:4,2:3) * y(2:4,6)
  2 个评论
Alexandra Harkai
Alexandra Harkai 2016-10-24
Since the example x array was initialised as an all-0 array, it looked like you wanted a numerical array. If that's not the case, you can always do num2cell(...) before the assignment.
Adam
Adam 2016-10-24
It's generally a very bad idea to have data structured in that way with a row and column like that (a table structure sounds more obvious if that is what you want), but you can still apply any of the solutions given with a bit of alteration.
Just pull out the part of the array you want and apply to that, then re-insert it, using num2cell and cell2mat either side of your operation and depending whether you have R2016b or not use bsxfun to do the multiplication.

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Ki Loius
Ki Loius 2016-10-24
I think I have another problem:
y is a 17x9 cell
x=cell2mat(y(2:3,2:5)) gives me the content of the cell in that range
but
x=cell2mat(y(2:4,2:5)) or x=cell2mat(y(2:3,2:6)) does not work. It says
Dimensions of matrices being concatenated are not consistent.
Ki Loius
Ki Loius 2016-10-24
I could solve my problem.
I had empty cells in my cell array. I filled them with 0 dann answer 3 worked.
Thank you!

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