Manipulating cell arrays based on index

how can I manipulate the elements of an array of cells based on index? for a double array, I can just do this:

>> j = zeros(4);
>> j(1:8) = 1;
>> j(9:16) = 8;
>> j

j =

       1     1     8     8
       1     1     8     8
       1     1     8     8
       1     1     8     8

However, for a cell array, I cannot

>> j = cell(4,1)

j = 

      []
      []
      []
      []

>> j{1:4} = [2 3 4]
The right hand side of this assignment has too few values to satisfy
the left hand side.

I could do this with a for loop easily, but I intend to extend this to a cell with ~400 elements.

After this is figured out, I'd also like to be able to do something based on the index, such as:

j = cell(100,1);
j(1:100) = ones(1:100,1);

[Stephen23]

You really need to read the documentation for ones, because providing it with a vector does not make any sense... it does not do what you think it does.

Also you should not use i or j for variable names, as these are both names of the inbuilt imaginary unit.

Answer 1

[Stephen23]

"However, for a cell array, I cannot"

Of course you can! Cell array indexing is covered here, and is well worth reading:

http://www.mathworks.com/help/matlab/matlab_prog/access-data-in-a-cell-array.html

But it depends what you expect. What you trying to do here is assign one array to the inside of multiple cells. This does not work. But you can allocate four cells to four cells (these are equivalent):

X(1:4) = {1,2,3,4}
X(1:4) = num2cell([1,2,3,4])

Or one cell (containing an array) to four cells:

X(1:4) = {[2,3,4]}

So if you want a cell array where every cell contains the same element, try this:

X = cell(100,1);
X(:) = {ones(100,1)}

[Noah Chrein]

Thank you for the swift answer! The last piece of code is exactly what I am looking for, however it doesn't work.

>> j = cell(4,1)

j = 

      []
      []
      []
      []

>> j{1:4} = {[2,3,4]}
The right hand side of this assignment has too few values to satisfy the left hand side.

[Stephen23]

Please see my edited answer, I made a mistake with the brackets.

[Brendan Hamm]

You actually want to use:

j(1:4) = {[2,3,4]} % Index using parenthesis

[Noah Chrein]

Ah yes, now this works! Thank you!

Answer 2

[Azzi Abdelmalek]

jj=cell(100,1)
jj(1:100) = num2cell(ones(100,1))

[Noah Chrein]

After doing this exactly calling jj{1} returns just 1, not ones(100,1), that is

jj{1} = [1]

whereas I want:

jj{1} = ones(100,1) = [1 1 ... 1]

[Azzi Abdelmalek]

jj=cell(100,1);
out=cellfun(@(x) ones(100,1),jj,'un',0)

[Noah Chrein]

Thank you! this works.