cell2table removes values from first column if string is a single character

Question

Suppose you have the following data:

A = [1,2,3;4,5,6];

headers = {'force', 'mass', 'acceleration'};
units = {'N','Kg','m/s^2'};

Let's say I want to convert it to a table, where headers will be the 'VariableNames':

table_of_data = cell2table([units; num2cell(A)]);
table_of_data.Properties.VariableNames = headers
table_of_data = 
    force    mass    acceleration
    _____    ____    ____________
    N        'Kg'    'm/s^2'     
            [2]     [3]         
            [5]     [6]

Note that the first two columns of A are removed. This is because MATLAB treats the single character N differently than 'Kg' and 'm/s^2'. If I insert a space after 'N ' I get:

table_of_data = 
    force    mass    acceleration
    _____    ____    ____________
    'N '     'Kg'    'm/s^2'     
    [1]      [2]     [3]         
    [4]      [5]     [6]

How can I get a proper table, with all elements displayed without inserting a space 'N '?

It's no problem to use a single character in units if I add more rows to the cell array, such as [headers; units; num2cell(A)], so the following works:

table_of_data = cell2table([headers; units; num2cell(A)]);
table_of_data(1,:) = [];
table_of_data.Properties.VariableNames = headers
table_of_data = 
    force    mass    acceleration
    _____    ____    ____________
    'N '     'Kg'    'm/s^2'     
    [1]      [2]     [3]         
    [4]      [5]     [6]

How can I solve this without turning to cumbersome workarounds?

Why not store your units in `table.Properties.VariableUnits`? — Suever, Sep 02 '16 at 18:45
What's happening is that it's implicitly converting the entire first column to `char`'s and `1` and `4` look like empty strings and for single chars, MATLAB removes the `''` around the string. — Suever, Sep 02 '16 at 18:47
I've realized that. It can be seen quite easily if you try to write it to a dat-file (it can be seen in Notepad for instance). It would be nice to avoid it though :) — Stewie Griffin, Sep 02 '16 at 18:51
It's ugly looking, but probably the easiest way to get what you want is to replace units with `units = { {'N'}, {'Kg'}, {'m/s^2'}};` — CKT, Sep 02 '16 at 18:52
@Suever. I'm writing this to a .dat file. `VariableUnits` aren't included when executing `writetable`. — Stewie Griffin, Sep 02 '16 at 18:55

Suever · Accepted Answer · 2016-09-02T19:03:08.567

This likely has to do with table's internal representation of the data. It seems like what it does is tries to vertically concatenate the data in a column and if the concatenation succeeds then it uses an array, otherwise it stores it as a cell .

In the case of a single character N and the numbers, 1 and 4, they can be concatenated without error; however, it converts them all to chars.

vertcat('N', 1, 4)

However, when you add the space, concatenation now fails

vertcat('N ', 1, 4)

And the output is displayed like a cell.

You have a few options:

Use table.Properties.VariableUnits to store the units rather than trying to incorporate the units into your table.
```
table_of_data.Properties.VariableUnits = units;
```

Display the units in the column headers

headers = {'force_N', 'mass_kg', 'acceleration_m_s2'};

Create a double-nested cell array to store all of the units, which explicitly causes it to be stored as a cell array internally.
```
table_of_data = cell2table([num2cell(units); num2cell(A)])
```

I believe it's "prior to _creating_ it". I don't think it has anything to do with the actual displaying. — Stewie Griffin, Sep 02 '16 at 18:57

cell2table removes values from first column if string is a single character

1 Answers1

Linked