Change table variable type

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

Answer 1

[Walter Roberson]

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()

[dleal]

thank you! Exactly what I needed

[dleal]

Hi Walter Roberson, the three solutions you mention above work, but could you please briefly explain what in MATLAB does not allow my suggested method to work?

tbl1(:,intCols) = varfun(@double,tbl1(:,intCols))

(I know in R and Python these are valid assignments).

[Steven Lord]

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]

I understand Steven, thanks for your answer, it is all clear now