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Strings are converted to cells during readtable

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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?

Accepted Answer

Stephen23
Stephen23 on 10 Jun 2022
Edited: Stephen23 on 10 Jun 2022
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"

More Answers (2)

Adam Danz
Adam Danz on 4 Jan 2024
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)

KSSV
KSSV on 10 Jun 2022
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)

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