How to convert a .csv file of cell array type to double?

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hello_world
hello_world 2018-7-4
编辑： Maria Battle 2021-12-27
I have multiple .csv files of type Cell. I have attached 3 of these files for illustration and a data.csv file of type double. These files are located in path C:\Users\Anonymous\Documents\MATLAB
I want to load them one-by-one and convert them to type double and then to save them in the same path. I tried different ways, such as, cell2mat, str2mat, str2double, str2num, cell2csv (file exchange), etc. but without success. cell2mat gives error, and str2num convert everything in the file to NaN. Yes, it is true that my .csv files have characters like !, ., _, etc., but I still need to find a way to use the same file name and do the conversion to type double/numeric.
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Stephen23
Stephen23 2018-7-4
编辑：Stephen23 2018-7-4
Converting to double, categorical, etc, are all red herrings. The question states "I want to load them one-by-one and convert them to type double and then to save them in the same path". Remove the "convert to type double" and the task is simply one of merging file data. This does not require converting data types, or possibly even anything to do with numericals at all.
If hello_world explains the actual task that they are trying to achieve, then we could help them with that.
http://xyproblem.info/
https://meta.stackexchange.com/questions/66377/what-is-the-xy-problem
hello_world
hello_world 2018-7-4
编辑：hello_world 2018-7-4
@Stephen Cobeldick My actual task is that I want to convert File.A_label.csv as given in my example to type double such that the converted file does not contain numeric entries, such as, 1s, 2s, 3s, etc.
Now, you are asking me why I want to do it? I think you ask this because once you know what is the next goal, you will switch to that problem rather than advising me how to do this conversion. I just want to see if this type of conversion is possible. I am not looking for help in post achieving type double conversion.
So I do not think that it is an XY problem as you have referenced. Walter Roberson's solution is almost close but not exactly what I want to achieve. Frankly speaking, I do not think that it is even possible.

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回答（2 个）

Walter Roberson
Walter Roberson 2018-7-4
Depending on what you are doing, you might want to use categorical(), or might simply want to use findgroups().
Note that several of the classification and neural network routines are happy to take a cell array of strings as labels.
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Walter Roberson
Walter Roberson 2018-7-4
Your task is not possible. MATLAB has no possibility of having an item that is simultaneously a double and a string. The only computer language I can think of at the moment which permits that is AWK and its successors such as GAWK.

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Maria Battle
Maria Battle 2021-12-27
编辑：Maria Battle 2021-12-27
Regarding hello_world's comment "str2num converts everything in the file to NaN": if you want to apply str2num or str2double to an entire table, it appears MATLAB expects each element or each variable to be specified. .
For example
t = table([1;2;3;4],{'5.1';'6.2';'7.3';'8.4'},{'9.1';'10.2';'11.3';'12.4'},{'13.1';'14.2';'15.3';'16.4'})
t.Var2 = str2double(t.Var2); % MATLAB converts a single column just fine
% Produces a NaN result
t2 = str2double(t(:, 2:4));
The following help page shows how to use varfun to specify variables or a for loop to specify elements.
https://www.mathworks.com/matlabcentral/answers/277113-how-to-convert-cell-array-into-double-in-table
Also note that cell2mat does not convert strings to numbers.

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