Subtraction of cell values with a fixed value

Hello,

I'm trying to subtract the fixed number 389.387 from every cell element and then find the smallest one in each group. My code so far:

value_r = value_r';

grouped = mat2cell( value_r, 1, diff( [0, find(diff(row_r) ~= 1), length(row_r)] ));

%% grouped is a cell with [1x19 double] [1x2 double] [1x3 double] [1x2 double] [1x2 double] [1x1 double] [1x3 double] [1x2 double] [1x2 double] [1x3 double]

for i = 1:length(b) 

    difference(i) = abs(grouped{i} - 389.387);
    
end

But I keep getting the error code "Unable to perform assignment because the size of the left side is 1-by-1 and the size of the right side is 1-by-19.". The for loop works, but i can't safe the results in another variable. Any ideas?

I'm using Matlab R2020b for academic use

Answer 1

[DGM]

You could use cellfun() if you wanted.

s = [1 39];
A = randi([1 20],s(1),s(2));
k = 100; % the number to subtract

blocksizes = [19 2 3 2 2 1 3 2 2 3];

C = mat2cell(A,s(1),blocksizes)

C = 1×10 cell array
    {[7 19 4 4 16 7 2 16 4 15 3 17 17 20 2 13 17 16 1]}    {[1 5]}    {[3 12 5]}    {[3 12]}    {[19 7]}    {[13]}    {[19 10 5]}    {[9 15]}    {[20 19]}    {[19 14 3]}

D = cellfun(@(x) x-k,C,'uniformoutput',false);
E = cell2mat(cellfun(@min,D,'uniformoutput',false))

E = 1×10

-99 -99 -97 -97 -93 -87 -95 -91 -81 -97

% if intermediate result D is not needed
F = cell2mat(cellfun(@(x) min(x-k),C,'uniformoutput',false))

F = 1×10

-99 -99 -97 -97 -93 -87 -95 -91 -81 -97

% minimizing first is faster
G = cell2mat(cellfun(@min,C,'uniformoutput',false))-k

G = 1×10

-99 -99 -97 -97 -93 -87 -95 -91 -81 -97

Lastly, the fastest way would be to avoid cell operations. If all the block sizes are the same, you can do that like this.

H = min(reshape(A(1:36),4,9))-k % note all the block sizes are identical 

H = 1×9

-96 -98 -97 -98 -99 -97 -97 -95 -91

[Bruce Rogers]

Hey DGM,

that's a good solution, thank you very much! But the code wouldn't work, if the cell has a different number of cell groups. How can I make this more variable?

[DGM]

Ah yeah. I forgot about that. I got this mixed up with about three similar answers on the same day. The last example really only works with fixed block sizes. I imagine you could jump through some hoops using NaN padding, but I don't see a reason to actually recommend it.

I edited for clarity and went ahead and used the block sizes in your question for the cell array example.

[Bruce Rogers]

No problem, you're right, i can just count first the number of groups and the length of the vector and then it's all variable! Thanks DGM!