How to replace several characters from string in julia - replace

Question

I have tried below function.
Example:
dna = "ACGTGGTCTTAA"
function to_rna(dna)
for (nucleotides1, nucleotides2) in zip("GCTA", "CGAU")
dna = replace(dna, nucleotides1 => nucleotides2)
end
return dna
end
Output: "UGGUGGUGUUUU", which is not expected.
Expected output: "UGCACCAGAAUU"
Can somebody point out what went wrong.

Answer 1

You're performing the replacement of each letter in sequence:
julia> function to_rna(dna)
for (nucleotides1, nucleotides2) in zip("GCTA", "CGAU")
dna = replace(dna, nucleotides1 => nucleotides2)
#show nucleotides1 => nucleotides2
#show dna
end
return dna
end
to_rna (generic function with 1 method)
julia> to_rna(dna)
nucleotides1 => nucleotides2 = 'G' => 'C'
dna = "ACCTCCTCTTAA"
nucleotides1 => nucleotides2 = 'C' => 'G'
dna = "AGGTGGTGTTAA"
nucleotides1 => nucleotides2 = 'T' => 'A'
dna = "AGGAGGAGAAAA"
nucleotides1 => nucleotides2 = 'A' => 'U'
dna = "UGGUGGUGUUUU"
"UGGUGGUGUUUU"
julia> dna
"ACGTGGTCTTAA"
That is, you can't distinguish an RNA C from a DNA C after the first step etc.
You'd want it to work in parallel -- somehow like this:
julia> to_rna2(dna) = map(dna) do nucleotide
NUCLEOTIDE_MAPPING[nucleotide]
end
to_rna2 (generic function with 1 method)
julia> NUCLEOTIDE_MAPPING = Dict(n1 => n2 for (n1, n2) in zip("GCTA", "CGAU"))
Dict{Char,Char} with 4 entries:
'A' => 'U'
'G' => 'C'
'T' => 'A'
'C' => 'G'
julia> to_rna2(dna)
"UGCACCAGAAUU"
This also removes the unnecessary work of iterating over the string four times.
replace is already able to do that by itself -- if you give it an array and pass it multiple replacement arguments:
julia> replace(collect(dna), NUCLEOTIDE_MAPPING...)
12-element Array{Char,1}:
'U'
'G'
'C'
'A'
'C'
'C'
'A'
'G'
'A'
'A'
'U'
'U'
To get back a string instead of an array, you just have to join it again:
julia> replace(collect(dna), NUCLEOTIDE_MAPPING...) |> join
"UGCACCAGAAUU"