Decision trees & continuous-valued attributes -

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how decision tree handle continuous valued attributes? know attributes such sex have 2 arcs denoting male or female. how continuous valued attributes such age? not possible create arcs each possible value? create age-range sets? example having 3 sub-branches labeled <18, <30, >30? if how decide on creation of these age-groups?

some algorithms cart evaluates possible splits using gini index or other impurity functions. sort attributes , @ impurity of each split. drawback of method is greedy, need @ every possible split. see image here.


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