Why I cant make a loop from the textfile I chose?

% creating a multidimensional array
files = dir('*txt') ;     % you are in the folder with text files 
N = length(files) ;
names = {files(:).name}' ;
iwant = cell(N,1) ;
for i = 1:N
    iwant{i} = importdata(files(i).name) ;
end
% select which element is needed
A = input('Please enter an element:');
% find the number of samples
n = length (A(:,1));
% step change for the wavelength
step = 0.02;
% wavelength which is at the centre
p = A(:,1);
% to make new wavelength for each of wavelength in the samples
for i=1:n
    new_wavelength(n) = p-step*10:step:p+step*10
end

I want to make a loop from all the row and first column from the element I chose but it gave me the respond below:

Please enter an element:iwant{2}(:,1) % this is the input i wrote
In an assignment  A(:) = B, the number of elements in A and B must be the same.

Error in saja (line 19)
    new_wavelength(n) = p-step*10:step:p+step*10

Where did I go wrong? Can someone figure it out? I will attached the folder that i have put in array.

Answer 1

[Bob Thompson]

new_wavelength(n) = p-step*10:step:p+step*10

new_wavelength(n) is only a single element, because n is a single value. new_wavelength is an array of size 1xn, but your indexing is calling only a single element of it.

p is an array of size nx1 (p is actually just a copy of the first column of A), and so you cannot fit an entire array into a single element of a double array. That's why you're getting the error.

[Mohamad Khairul Ikhwan Zulkarnain]

So what is the right command for me then? I want for each value in the first column to have 20 more new wavelength. How do I write command for that?

[Walter Roberson]

Do you want the second column to be the first column plus 20, and the third column to be the second column plus 20, and so on, with column #K being the first column plus (K-1)*20 ?

[Mohamad Khairul Ikhwan Zulkarnain]

I want to create a range of 20 new data for each data in the first column and second column. Thats why I try to use the command below:

for i=1:n
    new_wavelength(i) = p(:,1)-step*10:step:p(:,1)+step*10
end

But it doesnt work out. Could you help me with it?

[Walter Roberson]

p = A(:,1);
offset = step * (-10:10);
new_wavelength = bsxfun(@plus, p, offset);

This will create a matrix in which each row corresponds to a different entry in A(:,1). There will be 21 entries for each row (not 20 entries: remember the 0 relative offset in the middle.). If you want columns instead of rows, then use

new_wavelength = bsxfun(@plus, p, offset) .';

[Mohamad Khairul Ikhwan Zulkarnain]

Thank you! Appreciated!