# Convert double to categorical array

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Parichada Trairat on 16 Jun 2022
Commented: Peter Perkins on 17 Jun 2022
Hello,
I have a problem with convert double to categorical.
the matlab showed:
Error using categorical
Unable to create default category names. Specify category names using the CATEGORYNAMES input argument.
This is my code:
YTrain = trainYweekday';
YTrain = categorical(YTrain);
YTrain = num2cell(YTrain,1);
trainYweekday' is 1x360 double.
How can I convert trainYweekday to categorical?
Thank you very much.
Adam Danz on 16 Jun 2022
@Parichada Trairat thanks for the YTrain values but I deleted them from your question so my mouse scroll wheel doesn't catch on fire 🔥 🙂
Feel free to attach long data sets as files.

Adam Danz on 16 Jun 2022
Edited: Adam Danz on 16 Jun 2022
The function categorical can convert continuous data into categorical data. However, this function cannot categorize two numbers if the difference between them is less than 5e-5, unless their differences are 0.
Example:
categorical([pi, pi])
ans = 1×2 categorical array
3.1416 3.1416
categorical([pi, pi+5e-5])
Error using categorical
Unable to create default category names. Specify category names using the CATEGORYNAMES input argument.
To get around this, you must discretize the vector
vals = [pi, pi+5e-5];
categorical(discretize(vals, min(vals):1e-6:max(vals)))
See this MathWorks Support Team article for more details.
Also see this example from the categorical doc page that shows the use of discretize to prevent this problem.
##### 2 CommentsShowHide 1 older comment
Peter Perkins on 17 Jun 2022
The categorical function tries to make categories out of the unique values of whatever you give it. "Convert double to categorical" sometimes makes sense if you mean "convert continuous numeric data into categorical with one category for each unique numeric value." But if you run into this error, you almost certainly should be binning your continuous data using discretize instead.

R2022a

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