Check for equivalence of string and symbol - julia

Question

I have a vector of symbols a_sym of length N_sym and a vector of strings a_str of length N_str
a_sym contains symbols at each index, such as :H₅B₂O₆⁻
a_str contains strings at each index, such as H₅B₂O₆⁻
I would like to check for equivalence of a_sym and a_str to see which index the equivalence occurs in each vector.
I have tried to implement a loop to check these two vectors:
E = zeros(Int64,N_sym)
for i in 1:N_str
for ii in 1:N_sym
if a_sym[ii] == a_str[i]
E[ii] = i
end
end
end
Where E is my attempt to map equivalent indices, but my loop never detects the strings to be equivalent. How could this be remedied? (and perhaps simplified?)
For example:
a_sym = [:H₃BO₃ ,:H₄BO₄⁻ ,:Li⁺ ,:H₅B₂O₆⁻, :H₄B₃O₇⁻]
where N_sym would be 5, and:
a_str = ["O⁻","H₃BO₃","H₄BO₄⁻","H₅B₂O₆⁻","H₄B₃O₇⁻","H₃B₃O₆"]
where N_str would be 6. I require the loop to check both vectors and map the indices when there is equivalnce, for instance the index of H₃BO₃ in a_sym would be 1, and its index in a_str would be 2.
I expect a vector E = [2, 3, 0, 4, 5] which is filled with the indices of a_str, and 0 if a_str does not contain a match for a_sym

Answer 1

Symbols and strings are never equivalent:
julia> :a == "a"
false
So you have to convert either to the other first. I would write your function as follows using the builtin findfirst:
julia> E = [findfirst(==(String(b)), a_str) for b in a_sym]
5-element Array{Union{Nothing, Int64},1}:
2
3
nothing
4
5
(Although, as Przemislaw notes, converting the strings to symbols would likely be more efficient.)
nothing is what findfirst returns if it does not find anything. You can convert this to a default by broadcasting something:
julia> something.(E, 0)
5-element Array{Int64,1}:
2
3
0
4
5