cell2mat eliminating a column from cell array when performing conversion

Question

I have the following code:

% Code to import data from .csv files into cell arrays called strain_trans_data, strain_ax_data, and load_data

strain_trans_data = cell2mat(strain_trans_data);
strain_trans_data = strain_trans_data*-1; % trans strain to -trans strain
strain_ax_data = cell2mat(strain_ax_data);
load_data = cell2mat(load_data);
new_trans_data = [];
new_ax_data = [];
new_load_data = [];
regressions = {'File name','y-int axial','slope axial','y-int trans','slope trans','v'};

% Rest of the code...

The code imports data from some .csv files which I analyze by performing a linear regression. To perform the linear regression and to plot the data, I need to convert the cell arrays to matrices. When I import a lot of data (from more than 10 .csv, in my case I have 11 files), strain_trans_data = cell2mat(strain_trans_data); and strain_ax_data = cell2mat(strain_ax_data); work fine, they just convert the cell arrays to matrices. Since there are 11 sets of data, the cell arrays are nx11 and the final matrices are nx11.

For some reason, load_data = cell2mat(load_data); instead eliminates one column so the initial cell array is nx11 and the final matrix is nx10 instead. I tried with other sets of data (smaller than 10) and this problem seems to only occur in this instance. What is strange is that both strain_trans_data = cell2mat(strain_trans_data); and strain_ax_data = cell2mat(strain_ax_data); work fine, it's only the last conversion that gives a problem. Any idea why this might be happening?

Edit: I tried stepping into the cell2mat function to see what was happening and found the step where the problem happens. In the image below m is a nx11 cell

then for some reason it changes to a nx10 double. Could there be a problem with the data in the cell array?

Cris Luengo Cris Luengo · Accepted Answer · 2018-09-11T03:41:00

Without being able to see the cell array that you input into cell2mat I can only guess, but my guess would be that you have a column in the cell array with empty cells.

I can reproduce your issue this way:

C = num2cell(magic(4));
[C{:,3}] = deal([]);

C now looks like this:

C =
  4×4 cell array
    [16]    [ 2]    []    [13]
    [ 5]    [11]    []    [ 8]
    [ 9]    [ 7]    []    [12]
    [ 4]    [14]    []    [ 1]

Now we apply cell2mat:

A = cell2mat(C);

A looks like this:

A =
    16     2    13
     5    11     8
     9     7    12
     4    14     1

C as a 4x4 cell array, A is a 4x3 numeric array.

cell2mat eliminating a column from cell array when performing conversion

1 Answers