Find the number of non-empty cells in each row of a cell array

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Jim McIntyre 2022-11-17

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https://ww2.mathworks.cn/matlabcentral/answers/1854008-find-the-number-of-non-empty-cells-in-each-row-of-a-cell-array

编辑： Adam Danz 2022-11-30

I have a cell array of tables where each row contains data for one specimen and each column of that row contains results of repeated tests for that specimen. There are different numbers of tests in each row.

I would like to process each row based on the number of tests. How can I determine the number of cells in each row that contain tables? For example, the first row contains 12 cells, the second contains 14, etc.

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Answer 1

Adam Danz 2022-11-17

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https://ww2.mathworks.cn/matlabcentral/answers/1854008-find-the-number-of-non-empty-cells-in-each-row-of-a-cell-array#answer_1102698

编辑：Adam Danz 2022-11-17

在 MATLAB Online 中打开

Here's a demo that

creates a cell array of tables and empty cells
determines which cells contain a table
counts the number of tables per row

c = cell(3,4); 
c([1,2,3,4,6,10,12]) = {array2table(rand(5))}
c = 3×4 cell array
    {5×5 table}    {5×5 table }    {0×0 double}    {5×5 table }
    {5×5 table}    {0×0 double}    {0×0 double}    {0×0 double}
    {5×5 table}    {5×5 table }    {0×0 double}    {5×5 table }
y = cellfun(@istable, c)
y = 3×4 logical array
   1   1   0   1
   1   0   0   0
   1   1   0   1
nTablesPerRow = sum(y,2)
nTablesPerRow = 3×1
     3
     1
     3

If you'd rather count any cell that is not empty,

y2 = ~cellfun(@isempty, c)
y2 = 3×4 logical array
   1   1   0   1
   1   0   0   0
   1   1   0   1
nNonEmptiesPerRow = sum(y2,2)
nNonEmptiesPerRow = 3×1
     3
     1
     3

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Adam Danz 2022-11-18

编辑：Adam Danz 2022-11-30

在 MATLAB Online 中打开

> Is there a more-efficient way to do this?

Your approach is readable and reasonable so I don't see a need to change it. I can think of other approaches and if we were to do a proper investigation of their efficiencies, they might be a tad faster or a tad slower by but the difference wouldn't be big enough to sacrifice readability, IMO.

For example, here are two suggestions below. The first is merely preferential and easier to read. The second is an improvement on flexibility but is likely a tad slower.

for j=1:height(y) % <---- changed to height(), just my preference

for k=find(y(j,:)) % <--- no longer assumes empties are all at the end, but slower

...

end

Another idea is to reduce two for-loops to one for-loop which, IMO, is more readable.

% *not tested....

y = cellfun(@istable, data);

ind = find(y);

for i = ind(:)' % must be row vector

data{i}.FiltAccel=filter(Hd,data{i}.Accel);

data{i}.FiltSlip=filter(Hd,data{i}.Slip);

end

Jim McIntyre 2022-11-23

There are 113 tables in data{}. The first part looks like this:

>> ind=find(y);

>> for i = ind

data{i}

end

ans =

280×9 table

Time Speed Distance Acceleration RRSpeed PctSlipRR SW_Angle Throttle Gear

____ _____ ________ ____________ _______ _________ ________ ________ ____

0 0.32 0 0.15 0 0 1.5 21 1

0.01 0.35 0.01 0.13 0 0 1.5 21 1

0.02 0.37 0.01 0.13 0 0 1.5 21 1

0.03 0.39 0.02 0.12 0 0 1.5 21 1

0.04 0.39 0.02 0.12 0 0 1.5 21 1

: : : : : : : : :

2.75 4.8 9.95 0.17 5.6323 17.926 3 29.5 1

2.76 4.79 10.02 0.18 5.6581 17.388 3 29.5 1

2.77 4.8 10.09 0.18 5.6581 16.48 3 29.5 1

2.78 4.86 10.16 0.2 5.7739 18.408 3 29.5 1

2.79 4.93 10.23 0.2 5.7739 18.865 3 29.5 1

Display all 280 rows.

ans =

317×9 table

Time Speed Distance Acceleration RRSpeed PctSlipRR SW_Angle Throttle Gear

____ _____ ________ ____________ _______ _________ ________ ________ ____

0 0.33 0 0.13 0 0 -1.5 22.5 1

0.01 0.33 0.01 0.13 0 0 -1.5 22.5 1

0.02 0.33 0.01 0.13 0 0 -1.5 22.5 1

0.03 0.35 0.02 0.13 0 0 -1.5 23 1

0.04 0.36 0.02 0.13 0 0 -1.5 23 1

: : : : : : : : :

3.12 4.91 13.38 0.14 10.484 116.94 -6 34 2

3.13 4.95 13.45 0.12 10.079 106.69 -6 34 2

3.14 4.98 13.52 0.14 9.8829 101.64 -6 34 2

3.15 4.99 13.59 0.12 9.4256 91.573 -6 34 2

3.16 4.99 13.67 0.08 9.2232 87.22 -6 34 2

Display all 317 rows.

This causes the error:

>> for i = ind

data{i}.Speed

end

Intermediate brace '{}' indexing produced a comma-separated list with 113 values, but it must produce a single value when followed by subsequent indexing operations.

Jim McIntyre 2022-11-29

The ' transform definitely made the difference.

Y is a 7x18 logical, yet ind is a 113x1 double, and data{i} wants a 1x113.

From the help for find:

If X is a multidimensional array, then find returns a column vector of the linear indices of the result.

Thank you again for all your help on this!

Adam Danz 2022-11-30

Ah, of course. Thanks @Jim McIntyre. That's what I get for running code in my head rather than actually testing it 😊

I'll update my previous comment to avoid confusions for any future visitors.

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Find the number of non-empty cells in each row of a cell array

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