Little Bit Help Required Regarding Loop

Question

John Hock 2019-2-17

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https://ww2.mathworks.cn/matlabcentral/answers/445388-little-bit-help-required-regarding-loop

评论： Stephen23 2019-2-18

采纳的回答： Stephen23

Hi EveryOne

I am currently working on this code

a=[1 2 3]

b=[3 4 5]

c=[34 5 6 ]

for i=1:1:3;

C = {[a];[b];[c]};

d= cellfun(@(v)v(i),C)

end

And the output is

d =

1

3

34

d =

2

4

5

d =

3

5

6

Every time loop runs it updated the last results.

I just want to save all the values means every time when loop run it keep save the last results and save the new results in the new coloumn

When I use

d(i)= cellfun(@(v)v(i),C)

The code give error

In an assignment A(I) = B, the number of elements in B and I must be the same.

Please help in this matter

Thanks

Regards

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Stephen23 2019-2-17

编辑：Stephen23 2019-2-17

Note that these square brackets are totally superfluous:

C = {[a];[b];[c]};

All you need is:

C = {a;b;c};

You will notice that these superfluous square brackets are underlined by the MATLAB Editor:

https://www.mathworks.com/matlabcentral/answers/35676-why-not-use-square-brackets

Also there is no need to completely redefine C on every loop iteration: it is simpler and more efficient to just define it once before the loop.

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Answer 1

Stephen23 2019-2-17

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/445388-little-bit-help-required-regarding-loop#answer_361395

编辑：Stephen23 2019-2-17

"I just want to save all the values means every time when loop run it keep save the last results and save the new results in the new coloumn"

Why so complex? One simple concatenation gives exactly the same result:

>> d = [a;b;c]
d =
    1    2    3
    3    4    5
   34    5    6

Or, if your arrays are already in a cell array and you just need to concatenate them together:

>> tmp = {a;b;c}; % your cell array
>> d = vertcat(tmp{:})
d =
    1    2    3
    3    4    5
   34    5    6

https://www.mathworks.com/help/matlab/matlab_prog/comma-separated-lists.html

https://www.mathworks.com/matlabcentral/answers/320713-how-to-operate-on-comma-separated-lists

If you really want to use a slow and complex loop to do this:

>> d = nan(3,3); % preallocate
>> for k = 1:3, d(:,k) = [a(k),b(k),c(k)]; end
>> d
d =
    1    2    3
    3    4    5
   34    5    6

which could also be complicated even more with a cellfun call:

>> d = nan(3,3);
>> for k = 1:3, d(:,k) = cellfun(@(t)t(k),tmp); end
>> d
d =
    1    2    3
    3    4    5
   34    5    6

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Stephen23 2019-2-18

John Hock's "Answer" moved here:

@Stephen Cobeldick

Thanks alot sir for your time and help

Let me explain you a little bit more

I had a data from 26 channles of EEG

Lets assume 2560 points for each chanenl

i just want to read the 1st element of each channel and put it in a array

and then second element till 2560 element .

Will cancatenation is ok for this work?

And 1 more thing will you please help me a little bit more that after reading first element of all channels i also want to find minimum value,maximum value and their mean also.and the same for rest values

Thanks in advance

Stephen23 2019-2-18

@John Hock: assuming that each channel has exactly the same number of data points, then your best approach would be to concatenate them all into one numeric array. Then you can trivially call min, max, mean etc. with their optional dimension argument.

For example, where tmp is a cell array of identically-sized row vectors:

d = vertcat(tmp{:});
mean(d,1)
max(d,[],1)
min(d,[],1)

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