organising large sets of data into a irregular matrix

Question

judith schweimer 2019-3-7

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https://ww2.mathworks.cn/matlabcentral/answers/448849-organising-large-sets-of-data-into-a-irregular-matrix

回答： judith schweimer 2019-3-13

Hello,

I have a large data sets with of 40000+ samples, which are organised in 2 columns. The first colum tells me a cluster-number (column 1) by which I would like to sort, and the second a value is a time which I would like to allocated to the individual clusters.

the data looks something like:

A=[32 7.83425

32 8.0074

5 8.01005

5 8.0119

5 8.10775

19 8.1082

7 8.1085

4 8.1089]

I would like to organise this set into a matrix or table. One caveat is that the clusters are different sizes.

I have managed to get the individual cluster number out of my matrix, using the unique function.

I thought this would be similar to this thread:

https://uk.mathworks.com/matlabcentral/answers/19877-organizing-data-into-a-matrix-generating-a-matrix

However I am struggling to assign the values to the clusters because of the irregular number of values per cluster.

Can someone help me with this?

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Answer 1

Jos (10584) 2019-3-7

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https://ww2.mathworks.cn/matlabcentral/answers/448849-organising-large-sets-of-data-into-a-irregular-matrix#answer_364330

在 MATLAB Online 中打开

You can use cell arrays for this.

A=[ 32 7.83425
    32 8.0074
     5 8.01005
     5 8.0119
     5 8.10775
    19 8.1082
     7 8.1085
     4 8.1089 ]
[unA, ~, j] = unique(A(:,1)) ;
C = accumarray(j, A(:,2), [numel(unA),1], @(x) {x})
% The cell C{k} contains all values that belong to unA(k)

However, for some purposes you can also use a matlab table, for which dedicated functions, like splitapply, exist to operate on groups. This may worthy of some exploration on your site ...

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judith schweimer 2019-3-8

编辑：Jos (10584) 2019-3-8

在 MATLAB Online 中打开

Hi Jos, thanks for this, creating the cell array works very well! However, I would like to export the data within the cell array to either Excel or a csv format. so that I can import the data into another software package.

My cell array is a 30x1 cell array, the individual parts are not all the same size!

I have tried several versions, but I didn't get it to work, yet. And I mostly get an error message like this "Error using horzcat

Dimensions of arrays being concatenated are not consistent.

Error in readspiketimes2 (line 26)

fprintf(file,[sprintf(['%s'],C1{row,1:ncols-1}) C1{row,ncols} '\n']);"

Here is my code (it is only part):

[a1, ~, j] = unique(clusters(:,1 )) ; 
C = accumarray(j, B(:,2), [numel(a1),1], @(x) {x })% The cell C contains all spiketime values per cluster 
C1 = C'; % I have played with this whether it makes a difference of the array being horizontal or %vertical, but either gives me the error
C1 = cellfun(@string, C, 'UniformOutput', false); %convert doubles into strings
file = fopen('times.xlsx', 'w');
[nrows,ncols] = size(C1);
for row = 1:numel(C1)
   fprintf(file,[sprintf(['%s'],C1{row,1:ncols-1}) C1{row,ncols} '\n']);
end    
fclose(file);

judith schweimer 2019-3-8

Almost perfect, I just need to switch columns and rows of the myfile, I will try this later, else I have trouble importing the data into Excel due to too long rows.

Thank you very much!