Change table variable type

Question

dleal 2022-3-30

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1684679-change-table-variable-type

评论： dleal 2022-3-31

Hello,

I am trying to change all variables in a table from int64 to double. I know I should use the "double" function, but for some reason it is not working. Please keep in mind I will be changing multiple columns from int to double. Here is an example:

tbl1 = table(int64(randi([1,100],[10,1])),randn([10,1]),'VariableNames',["x1","x2"]);
tbl1.x1 % verify that x1 is in fact int64
ans =
  10×1 int64 column vector
   44
   39
   77
   80
   19
   49
   45
   65
   71
   76
intCols = varfun(@isinteger,tbl1,'OutputFormat','uniform');  % get all integer columns in the table, in my case there are several
tbl1(:,intCols) = varfun(@double,tbl1(:,intCols));  % apply double to all columns and reassign them to the table
tbl1.x1  % in my case, they are still of the type int64
ans =
  10×1 int64 column vector
   44
   39
   77
   80
   19
   49
   45
   65
   71
   76
   
   

What am I doing wrong? thank you

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Answer 1

Walter Roberson 2022-3-30

0
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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1684679-change-table-variable-type#answer_930804

在 MATLAB Online 中打开

You need to replace the entire varible using dot syntax. For example,

tbl1.x1 = double(table1.x1);

to do that for several variables, you would pretty much need to loop using dynamic field names.

Alternatives:

If you do not mind potentially reordering the fields, then you could

notIntCols = setdiff(1:width(tabl1), IntCols);
tabl1 = [tabl1(:,notIntCols), array2table(double(tabl1(:,IntCols)), 'VariableNames', tabl1.Properties.VariableNames(IntCols))]

and you could probably do the same thing using addvars() https://www.mathworks.com/help/matlab/ref/table.addvars.html

Another approach would be to use table2cell(), replace the IntCols columns in the cell with double() of those columns, then cell2table()

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Steven Lord 2022-3-31

在 MATLAB Online 中打开

When you use indexed assignment, MATLAB tries to convert the quantity being assigned (on the right) into the type of the quantity being assigned into (on the left.)

x = int8(1:5)
x = 1×5
   1   2   3   4   5
x(1) = pi
x = 1×5
   3   2   3   4   5

In that code, pi returns a double so when it is assigned into x using indexed assignment MATLAB converts that double into the int8 value 3 then performs the assignment. So your varfun worked, but then MATLAB immediately converted the double results back to the original type of those variables, int64.

dleal 2022-3-31