Change table variable type

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dleal
dleal on 30 Mar 2022
Commented: dleal on 31 Mar 2022
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

Accepted Answer

Walter Roberson
Walter Roberson on 30 Mar 2022
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()
  4 Comments
Steven Lord
Steven Lord on 31 Mar 2022
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
dleal on 31 Mar 2022
I understand Steven, thanks for your answer, it is all clear now

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