Julia - Rewriting a CSV - csv

Question

Complete Julia newbie here.
I'd like to do some processing on a CSV. Something along the lines of:
using CSV
in_file = CSV.Source('/dir/in.csv')
out_file = CSV.Sink('/dir/out.csv')
for line in CSV.eachline(in_file)
replace!(line, "None", "")
CSV.writeline(out_file, line)
end
This is in pseudocode, those aren't existing functions.
Idiomatically, should I iterate on 1:CSV.countlines(in_file)? Do a while and check something?

Answer 1

If all you want to do is replace a string in the line, you do not need any CSV parsing utilities. All you do is read the file line by line, replace, and write. So:
infile = "/path/to/input.csv"
outfile = "/path/to/output.csv"
out = open(outfile, "w+")
for line in readlines(infile)
newline = replace(line, "a", "b")
write(out, newline)
end
close(out)
This will replicate the pseudocode you have in your question.
If you need to parse and read the csv field by field, use the readcsv function in base.
data=readcsv(infile)
typeof(data) #Array{Any,2}
This will return the data in the file as a 2 dimensional array. You can process this data any way you want, and write it back using the writecsv function.
for i in 1:size(data,1) #iterate by rows
data[i, 1] = "This is " * data[i, 1] # Add text to first column
end
writecsv(outfile, data)
Documentation for these functions:
http://docs.julialang.org/en/release-0.5/stdlib/io-network/?highlight=readcsv#Base.readcsv
http://docs.julialang.org/en/release-0.5/stdlib/io-network/?highlight=readcsv#Base.writecsv