Strings are converted to cells during readtable

Question

Bill Tubbs 2022-6-10

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1737610-strings-are-converted-to-cells-during-readtable

回答： Adam Danz 2024-1-4

I am incrementally saving data to a csv file which includes strings:

data = table("string1", "string2");
writetable(data, "data.csv");

Later on:

data_from_file = readtable('data.csv')

data_from_file =

1×2 table

Var1 Var2

___________ ___________

{'string1'} {'string2'}

Note that the data are now char arrays in cells.

This is causing lots of problems, for example when I try to join the old data with the new:

new_data = table("string1", "string2");
data = outerjoin(data_from_file, new_data, 'MergeKeys', true)

Error using tabular/outerjoin (line 152)

Left and right key variables 'Var1' and 'Var1' are not comparable because one is

a non-cell.

Is there a way to avoid this problem or convert the chars back to strings after readtable?

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KSSV 2022-6-10

Show us your new_data.

Bill Tubbs 2022-6-10

在 MATLAB Online 中打开

E.g.

new_data = table("string1", "string2");

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Answer 1

Stephen23 2022-6-10

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https://ww2.mathworks.cn/matlabcentral/answers/1737610-strings-are-converted-to-cells-during-readtable#answer_982760

编辑：Stephen23 2022-6-10

在 MATLAB Online 中打开

The simple solution is to specify the TEXTTYPE option when importing:

data = table("string1", "string2");
writetable(data, "data.csv");
data_from_file = readtable('data.csv', 'TextType','string')
data_from_file = 1×2 table
      Var1         Var2   
    _________    _________

    "string1"    "string2"

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Bill Tubbs 2022-6-10

Great. Thanks.

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Answer 2

Adam Danz 2024-1-4

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https://ww2.mathworks.cn/matlabcentral/answers/1737610-strings-are-converted-to-cells-during-readtable#answer_1383416

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When using the readtable(filename,opts,Name,Value) syntax, only a limited number of name-values pairs are available as input arguments and TextType is not one of them. If you are using the import options object and would like to enforce strings for text type, specify this name-value pair as an argument in detectImportOptions()

opts = detectImportOptions(filename,'TextType','string'); 
T = readtable(filename,opts)

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Answer 3

KSSV 2022-6-10

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1737610-strings-are-converted-to-cells-during-readtable#answer_982755

在 MATLAB Online 中打开

You can convert cell into a string and then use join.

data = table("string1", "string2");
writetable(data, "data.csv");
data_from_file = readtable('data.csv') ;
for i = 1:width(data_from_file)
    data_from_file.(i) = string(data_from_file.(i)) ;
end
new_data = table("string3", "string4");
data = outerjoin(data_from_file, new_data, 'MergeKeys', true)