Converting nominal attribute to numeric value using Weka

Question

Suppose nominal attribute is Outlook which contains three values Sunny , Overcast and Rainy. I want to convert this values of outlook attribute in numeric form i.e. 1,2,3 (order can be change). I saw one filter nominaltobinary in weka but this will create three columns. I don't want to create separate column for each value. How I can do this using Weka.

because some model will give error if input variable contains non-numeric values. — neha pawar
That is true but i think that applies for string attributes and not for nominal ones. I think nominal are converted to numbers internally. What model are you using? — xro7
but when I am loading this kind of data in Weka then some of the models will get disabled — neha pawar

Prateek Paranjpe Prateek Paranjpe · Accepted Answer · 2018-05-07T06:24:48

In the ARFF, if you are using it, you can have a comment which specifies what the values of the "Outlook" attribute are.

For example, you ARFF can contain this comment at the top -

%% Numeric values for the "Outlook" Attribute
%%   Sunny = 1
%%   Overcast = 2
%%   Rainy = 3
%%   Windy = 4

Then you can define the attribute as -

@attribute Outlook {1,2,3,4}

I dont think there is a way to do this in the UI. But you can use a text editor to edit the ARFF itself.

Converting nominal attribute to numeric value using Weka

2 Answers