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Change table variable data type

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Nikhil Tawakley
Nikhil Tawakley 2017-7-7
评论： yunyu Hu 2020-11-5
I used readtable() to read a text file into a table. One of the columns of the table was read (by default) as a double rather than a string. How does one change a columns datatype within a table?

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采纳的回答

Sean de Wolski
Sean de Wolski 2017-7-7
Change it before reading it in by modifying the options passed to readtable.
https://www.mathworks.com/help/releases/R2017a/matlab/ref/detectimportoptions.html
Or
t.Var1 = num2str(t.Var1)
  2 个评论
Nikhil Tawakley
Nikhil Tawakley 2017-7-7
The approach to modifying the read options was what I tried first but unfortunately detectimportoptions doesnt seem to work with 2016a...
num2str worked though so the issue is resolved...thanks!
Peter Perkins
Peter Perkins 2017-7-7
Without meaning to contradict Sean, num2str is almost certainly not what you want, at least not by itself. It is a very old function that creates a char matrix, which will likely be pretty awkward to work with. One possibility is to apply cellstr to that char matrix, another (if you're using a recent version of MATLAB) would be to convert using the string function (as in, string, the new class).

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更多回答（2 个）

Jeffrey Daniels
Jeffrey Daniels 2020-6-4
fileName = table.xlsx;
opts = detectImportOptions(fileName);
opts.VariableTypes{15} = 'char'; % This will change column 15 from 'double' or whatever it is to 'char', which is what you want.
new_table = readtable(fileName,opts);
Peter Perkins
Peter Perkins 2017-7-7
readtable also accepts a Format parameter that would allow you to override the automatic type detection.
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Nikhil Tawakley
Nikhil Tawakley 2017-8-29
I'm referring to the data types of the variables in a table. For example, a Table with variables: Name and Age with datatypes String and Integer respectively.
Is it possible to "copy" the datatypes from one table and then use them while creating another table? Continuing from the example above, if there's another table with variables: Item Name & Quantity, is it possible to "copy-paste" the datatypes String and Integer from the previous table?
Walter Roberson
Walter Roberson 2017-8-29
No, it is not possible to copy-paste datatypes. However, you could use
old_class = arrayfun(@class, OldTable.VariableName, 'Uniform', 0);
new_variable = arrayfun(@(value, newclass) cast(value, newclass), NewTable.VariableName, old_class, 'uniform', 0);
NewTable.VariableName = new_variable;
This assumes that each entry in the variable is a potentially different type -- which would not be the case for numeric entries for example. If you have numeric entries, then
NewTable.VariableName = cast( NewTable.VariableName, class(OldTable.VariableName) );

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