Help Changing Class/Type In A Table

Question

Kristine 2025-5-28

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2177360-help-changing-class-type-in-a-table

评论： Kristine 2025-6-4

Hi y'all,

How do I change the class/type of values in a column into datetime? They were added as datetime going in. When I go to access the file after and check the class, it indicates the variables are catigorical. Why does this happen?

Thank you!

8 个评论
显示 6更早的评论隐藏 6更早的评论

Kristine 2025-5-30

在 MATLAB Online 中打开

The code being used to create tables in datetime is shown below. The code is doing more than just adding datetime, but I added all potentially relavant code I think @Walter Roberson Is this helpful. I believe it should create columns with datetime, and I'm not sure why it isn't so.

% Adding datetime columns - using the file name for context. 
function [output] = add_datetime_column(reference_file, filename) 
    [filepath, name, extention] = fileparts(filename); % access file info to extract name of file
    parts_of_name               = extract(name, digitsPattern) ; % extract only the numbers in the name  
    date_only_cell     = parts_of_name(1) ; % define the first set of extacted numbers as date 
    date_and_time_cell = strcat(date_only_cell, time_only_cell) ; % combine the date and time cells into one 
    
    in_format_datetime = 'yyyyMMddHHmmss' ; % tell MATLAB how the cell data is formated, and it's convert to string
    convert_datetime   = datetime(date_and_time_cell, 'InputFormat', in_format_datetime) ; % convert cell data into datetime format/type/class
    dt_datetime       = datetime(convert_datetime, 'Format', 'MM-dd-yyyy hh:mm:ss') ;
    dt_date_only      = datetime(convert_datetime, 'Format', 'MM-dd-yyy') ; 
    repeat_number           = height(reference_file) ; % define # of rows in file to print datetime in a column that same number of times
    reference_file.Datetime = repmat(dt_datetime,  repeat_number, 1); % add column with datetime informaion 
    reference_file.DateOnly = repmat(dt_date_only, repeat_number, 1) ;
    
    output                  = reference_file ; 
end
% Runs multiple functions on each file. 
% Not All Defined Functions In This Function Are Shown Above
function []  = each_day_table(folder_referenced, output_folder_location)
   dimention = size(folder_referenced) ; % returns a row vector whose elements are the lengths of the corresponding dimensions 
   % for loop to process each individual file in the folder instead of going through all the files at once
   for i = 1:dimention(2) % (2) is referencing the second value given by size, which is the length (number of rows) ∴ number of files
       % accessing each file in the folder/diractory 
       datastore_result = datastore(folder_referenced(i)) ; % accesses files 
       original_data    = readall(datastore_result) ; % interprets files % making everything into one gant file, that's why it's so slow
       
       with_datetime    = add_datetime_column(original_data, folder_referenced(i)) ; 
       
       new_table        = new_table_useful_data(with_datetime) ; 
       no_zeroz         = remove_zeros(new_table) ;
       no_ESD_over_150  = remove_ESD_greater_150(no_zeroz) ;
      
       [~, name, ext] = fileparts(folder_referenced(i)) ; % ~ is used since that field is not references, so MATLAB knows to skip it
       output_filename = fullfile(output_folder_location, "new_" + name + ext) ; % defining path to directory, and how the file should be named
       writetable(no_ESD_over_150, output_filename) % Saving files 
   end 
end
% Create list of files to loop through
folder_with_files = dir(input_folder_location) ; % define directory where files are 
filenames         = fullfile({folder_with_files.folder}, {folder_with_files.name}) ; % access file path and name information  
csvFiles          = endsWith(filenames, '.csv') ;  % use logi → determining which values end in .csv (fullfile provides axtra info we don't want)
filenames         = filenames(csvFiles) ; % create cell array with all file names
% Running the functions.
each_day_table(filenames, output_folder_location) ; 

Cris LaPierre 2025-6-4

编辑：Cris LaPierre 2025-6-4

在 MATLAB Online 中打开

new_table        = new_table_useful_data(with_datetime) ; 
no_zeroz         = remove_zeros(new_table) ;
no_ESD_over_150  = remove_ESD_greater_150(no_zeroz) ;

These 3 data processing functions are also not defined in the shared code either.

Kristine 2025-6-4

These were other functions that remove rows of data that are unrelated to adding datetime columns to the files.

But I did resolve my own issue by switching "MM-dd-yyyy" to "MM/dd/yyyy". I changed nothing else. Now the columns are interpreted as having datetime values. A frustratingly simple solution, though I still don't understand why my code didn't work this way before.

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

Cris LaPierre 2025-5-29

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2177360-help-changing-class-type-in-a-table#answer_1565555

在 MATLAB Online 中打开

The best solution would be to fix how your data is imported. Then you don't hvae to convert it.

You could use convertvars, or just use datetime directly on the table variable

T.A = datetime(T.A,'InputFormat',infmt)

infmt should be set to match the current data. Since your data is categorical, you likely first need to convert it to a string or numeric data type. We could be more specific if you shared your data and code.

8 个评论
显示 6更早的评论隐藏 6更早的评论

Kristine 2025-6-4

@Cris LaPierre This is just a simplification on my code, but still results in a column of categorical values instead of datetime for me.

Cris LaPierre 2025-6-4

This code does not create categorical values. The code out.DateOnly.Format would throw an error. Are you sure the values are categoricals?

Can you identify where your code diverges from this example? Better yet, share your implementation of this approach.

请先登录，再进行评论。

Help Changing Class/Type In A Table

8 个评论
显示 6更早的评论隐藏 6更早的评论

回答（1 个）

8 个评论
显示 6更早的评论隐藏 6更早的评论

另请参阅

类别

标签

产品

版本

Community Treasure Hunt

Help Changing Class/Type In A Table

8 个评论 显示 6更早的评论隐藏 6更早的评论

回答（1 个）

8 个评论 显示 6更早的评论隐藏 6更早的评论

另请参阅

类别

标签

产品

版本

Community Treasure Hunt

8 个评论
显示 6更早的评论隐藏 6更早的评论

8 个评论
显示 6更早的评论隐藏 6更早的评论