Count how many different values a list takes in Mathematica

Question

I would like to get the number of different values found in a List.

For example:

The output for the List a={1,2,3,4,5} would be 5 whereas it would b

Answer 1

Use DeleteDuplicates (or Union in older versions) to remove duplicate elements. You can then count the elements in the returned list.

In[8]:= Length[DeleteDuplicates[a]]
Out[8]= 5

In[9]:= Length[DeleteDuplicates[b]]
Out[9]= 2