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

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Song Lyu
Song Lyu 2022-6-29
编辑： Stephen23 2022-6-29
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}

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回答（3 个）

KSSV
KSSV 2022-6-29
编辑：KSSV 2022-6-29
Let A be your cell array of size 7365x60 where each cell has 1x7 array.
B = cell2mat(A) ;
iwant = B(:,2:7:end) ;
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KSSV
KSSV 2022-6-29
Ran in:
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

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Walter Roberson
Walter Roberson 2022-6-29
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
Stephen23
Stephen23 2022-6-29
编辑：Stephen23 2022-6-29
"... 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.

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