assume t is the vector, following operation gives the result you want
nonzeros(t.*(1-sign(abs(imag(t)))))
***************************************************************
>> t=[1 2 3 4 5+ rand*i]
t =
Columns 1 through 3
1.0000 2.0000 3.0000
Columns 4 through 5
4.0000 5.0000 + 0.9501i
>> nonzeros(t.*(1-sign(abs(imag(t)))))
ans =
1
2
3
4
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