How do i get multiple values all at once from cell array?

Hi,

I have a 7365x60 cell, and there are 1x7 cell in every single block of the big one, like the image shown below:

here is the question, how can i get the second value from the 1x7 cell all at once without using cellfun and for loop(cause they are slow), for example, i want to get f from the Trajectory_Data (has 7365x60 cell) which is shown below, but when i run the code below, i got the error:"Expected one output from a curly brace or dot indexing expression, but there were 7365 results.",i dont know how to get all the second value from the cell (there would be 7365x60 = 441900 values in total),can anyone help me?

f = Trajectory_Data{:,1}{:,2}

Answer 1

[KSSV]

Let A be your cell array of size 7365x60 where each cell has 1x7 array.

B = cell2mat(A) ;
iwant = B(:,2:7:end) ; 

[Song Lyu]

i tried this one before, and i got 'cell2mat does not support cell arrays xontaining cell arrays or objects'.

[KSSV]

What each cell 1x7 has?

If you are running a loop are you intiailizng it? Loop will be faster, it wont be slow.

[Stephen23]

"What each cell 1x7 has?" doesn't really matter:

C = {{1,2,3};{4,5,6};{7,8,9}}

C = 3×1 cell array
    {1×3 cell}
    {1×3 cell}
    {1×3 cell}

D = cell2mat(C)

Error using cell2mat
CELL2MAT does not support cell arrays containing cell arrays or objects.

[KSSV]

Ohhh yes.....I took it as:

C = {[1,2,3];[4,5,6];[7,8,9]} ;
D = cell2mat(C)

D = 3×3

1 2 3 4 5 6 7 8 9

[Song Lyu]

thx KS, i got some idea from this one

Answer 2

[Walter Roberson]

Your options:

• loop
• cellfun
• arrayfun (effectively the same as cellfun)
• cell2mat to form a 3d array, and then index; this is very likely going to be slower than cellfun
• cat() the contents of the cell together along some dimension, process the results, and reshape() afterwards; this is very likely going to be slower than cellfun

[Song Lyu]

thx, i'll try the last one later

Answer 3

[Stephen23]

"... for loop(cause they are slow)"

A well-written loop will be fast enough, e.g. where C is your cell array and assuming that the nested cells contain scalar numerics:

M = nan(size(C));
for k = 1:numel(C)
    M(k) = C{k}{2};
end

Better data design would store such regular data in one numeric array, which would make this task trivial and fast.

[Song Lyu]

is the 'C' refers to Trajectory_Data?

[Stephen23]

yes, just use the name of your cell array.

[Song Lyu]

Thx, i'll try this later