Access data from a cell array

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Rajvi Amle 2021-7-14

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评论： Rajvi Amle 2021-7-17

I have a cell array of 1x10 where each of the 10 arrays are matrices of 138x18. If I want to access the data of each of the cells but just want to calculate the sum of (138,1) and (138,2) from each arrays then how do I calculate and how can I access it?

I tried below to get access through the cell as shown below:

x- 1x10 cell- 138x18 double

X=x{1,10};
m_Au_A1=X(:,1);
m_Au_V1=X(:,2);

I want to calculate the sum of (138,1) and (138,2) from each arrays of cell. How that can be done? Any help would be really appreciated. Thank you in advance.

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Rajvi Amle 2021-7-14

@Devanuj Deka Sorry for my incovenience and making a confusion in a question. Yes, I want the column vector containing the element wise sum of the entire first and and second colomn in each array.

Devanuj Deka 2021-7-15

Thanks for clarifying @Rajvi Amle. I have posted an answer with a solution, please check if this is what you wanted.

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Answer 1

Devanuj Deka 2021-7-15

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编辑：Devanuj Deka 2021-7-15

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@Rajvi Amle, you can try this:

load x  % Load the data
Sum = cell(1,10);   % Initialize a 1x10 cell array which will store the summed columns from each matrix in 'x'.
for i = 1:10    % For the i'th cell in 'x'
    mat = x{i}; % extract the matrix
    Sum{i} = mat(:,1) + mat(:,2);   % store the sum of the first two columns
end

Here 'Sum' will be a 1x10 cell array, where the i'th cell will store a column vector which is the sum of the first two columns of the matrix in the i'th cell of 'x'. I hope this helps.

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Devanuj Deka 2021-7-16

编辑：Devanuj Deka 2021-7-16

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@Rajvi Amle, If you want to calculate the mean, you'll have to add NaN values to the shorter columns so that all columns in Sum are of equal dimensions. For that, you'll have to modify the section inside the for loop:

for i = 1:10    % For the i'th cell in 'x'
    mat = x{i}; % extract the matrix
    mat_sum = mat(:,1) + mat(:,2);   % store the sum of the first two columns in an array
    mat_sum(end+1:139) = missing;    % Add NaN values to shorter columns to make them 139x1, which is the dimensions of the longest column in 'x'
    Sum{i} = mat_sum;   % Store this modified column to the i'th cell of Sum.
end

I used m = missing to fill NaN values. See this MATLAB Answer solution for clarity on how to use it: https://in.mathworks.com/matlabcentral/answers/647178-how-to-add-nan-values-to-a-matrix#answer_543968

Now all cells of Sum have equal dimensions. So using A = cell2mat(C), we can make a 139x10 matrix, on which we can directly apply the M = mean(A,dim) function.

Sum_array = cell2mat(Sum_col);
col_mean = mean(Sum_array,2,'omitnan'); % 2nd argument specifies the dimension along which the sum is to be calculated. Setting it as '2' will calculate the sum along the rows, giving the output as a 139x1 column.

'omitnan' will ensure that ALL the elements are summed - even the last elements in the longer columns.

If you don't pass any 3rd argument in mean, the default parameter will be 'includenan', which will give a NaN value in the output if any column has NaN in that row. For example, the shortest column in 'x' has 134 rows - which means that rows 135-139 in that column are NaN. Without specifying 'omitnan', the output col_mean will have NaN in the last 5 rows, even though other columns might have numeric values in those rows.

Rajvi Amle 2021-7-16

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Fig6_CI.png

@Devanuj Deka. Yes now I got an answer for mean as I expected. I calculate standard of deviation and confidence interval based on the mean. But my graph (attached as Fig6_CI) shows only a single line instead of showing three lines as upper bound, mean and the lower bound. Following is my code I calculated std and CI so far: Could you please help me with this?.

Sum_col = cell(1,10);   % Initialize a 1x10 cell array which will store the summed columns from each matrix in 'x'.
for i = 1:10        % For the i'th cell in 'x'
    T=t{i};
    T(end+1:139)= missing;
    mat = x{i};     % extract the matrix
    mat_sum= mat(:,1) + mat(:,2);   % store the sum of the first two columns
    mat_sum(end+1:139) = missing;
    Sum{i} = mat_sum;
end
Sum_array = cell2mat(Sum);
col_mean = mean(Sum_array,2,'omitnan');
% Confidence interval of 95% for simulated data
std=col_mean/size(Sum_array,2);                     % std dev of mean(y) is mean(y)/nObs
% ts = tinv([0.025;  0.975],length(x1)-1);      % T-Score
CI95 = [col_mean col_mean + 1.96.*(std/sqrt(length(mat_sum))) col_mean - 1.96.*(std/sqrt(length(mat_sum)))] ;

Rajvi Amle 2021-7-17

@Devanuj Deka Could you please help me with this if possible? This could be really helpful because i am working on my project and I am totally new in Matlab and trying to learn it.

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Answer 2

ANKUR KUMAR 2021-7-14

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Let us create a random data.

random_data_cell=arrayfun(@(x) rand(138,18), 1:10, 'uni',0);

Let merge these data set in a matrix.

random_data_matrix=cat(3,random_data_cell{:});
size(random_data_matrix)
ans = 1×3
   138    18    10
% "I want to calculate the sum of (138,1) and (138,2) from each arrays of cell."
sum_of_138_1=sum(random_data_matrix(138,1,:))
sum_of_138_1 = 5.7619
sum_of_138_2=sum(random_data_matrix(138,2,:))
sum_of_138_2 = 3.4424

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Rajvi Amle 2021-7-14

@ANKUR KUMAR Sorry for my incovenience and mistakenly made a confusion in a question. I want the column vector containing the element wise sum of the entire first and and second colomn in each array.

ANKUR KUMAR 2021-7-14

编辑：ANKUR KUMAR 2021-7-14

在 MATLAB Online 中打开

If you want to calculate the element wise sum, you can do it using the sum commands.

random_data_cell=arrayfun(@(x) rand(138,18), 1:10, 'uni',0);
random_data_matrix=cat(3,random_data_cell{:});
output=sum(random_data_matrix,3);
output
output = 138×18
    5.9721    5.4324    6.1655    4.4693    4.7727    5.7600    5.7924    5.5296    3.4552    5.3622    5.2822    6.8909    6.3871    4.5325    6.0799    4.7366    4.5823    5.3439
    4.5680    5.1044    3.8329    4.1000    6.6097    3.6770    4.1740    4.1137    5.9776    2.2656    4.5354    5.6484    4.2640    3.4529    5.0674    4.1760    4.9397    5.4225
    4.0440    4.0330    2.7096    4.4737    4.7923    4.8489    3.7870    4.8415    4.1043    5.1490    2.5537    5.4141    4.1984    5.1140    5.3451    5.3463    4.5572    5.0309
    4.0869    4.5015    5.9514    5.2031    3.4604    5.1385    5.5002    4.3508    5.4030    6.8004    4.6312    4.2704    4.8556    6.2446    4.5646    4.4551    3.9234    5.3623
    4.4039    5.4754    5.7783    3.5712    6.6286    4.8854    4.6261    5.3618    6.3978    6.9742    5.0644    5.9297    5.1274    4.4751    5.1649    3.7136    5.3540    3.2868
    7.5646    5.1302    4.7648    4.7789    6.0271    6.0025    5.5054    5.1250    4.6288    5.6412    5.0644    5.7957    5.3603    4.2789    5.3654    3.3256    5.2350    5.0227
    6.2739    4.5899    5.0476    5.5893    5.4855    4.8651    4.5546    4.8745    4.7439    8.0537    4.8122    6.4072    3.0733    5.1822    3.7056    6.1357    4.8739    5.3994
    5.0761    3.7176    5.6164    5.1590    5.4305    5.4357    5.0424    5.4848    5.5599    5.2829    4.6477    3.5005    4.6719    4.4396    5.6583    5.7473    5.0443    6.3915
    4.5823    4.8743    4.5528    4.9836    3.7416    6.4809    5.1090    5.7665    4.7820    4.4281    4.3189    3.8533    4.4411    3.8667    5.5423    4.9134    5.7209    5.3886
    4.5839    4.3828    5.0645    5.3717    4.6212    5.9840    4.5980    6.1460    5.1197    6.8984    6.1678    4.1784    5.1346    5.4579    3.3217    5.2189    5.0166    5.4038
size(output)
ans = 1×2
   138    18

If this is not the expected output, please let us know the dimension of your expected output. What would be the dimension of the output you are expecting?

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Access data from a cell array

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