Question

How to get the oddly indexed elements in a list? I am thinking of Select, but did not find anything returning an element’s position, especially considering there are repetitive elements in the list.

Also in general, how to select those elements whose indices satisfy some certain conditions?

Answer 1

There are a lot of ways, here are some of them:

In[2]:= a = Range[10];le = Length@a;

In[3]:= Table[a[[i]], {i, 1, le, 2}]

In[5]:= Pick[a, Table[Mod[i, 2], {i, 1, le}], 1]

In[6]:= a[[1 ;; le ;; 2]]

In general, with Pick[] (as an example) you can model any conceivable index mask.