Julia Create Column name from a variable when writing to a csv file - csv

Question

I'm trying to write a column name which has a variable. The other thing Im trying to get is the append function column-wise.
CSV.write("File_Name.csv",(;"column$i"::String=sort(val)),append=true)
where i is generated in for loop.
Also, how to append in next column? e.g. if there are 2 columns
column 1 | column2 |
then whats the way to add new column next to them as column 3?

Answer 1

That's a pretty unusal way of going about things, and the right answer is probably to change your approach more fundamentally - probably building up the table in a reasonable format in your code, and then writing out when you have it.
Fundamentally I believe you can't append columns to csv files, the append keyword works on a row-basis. You can transpose whatever you're reading in though, so you could just append your columns as rows and then read in transposed.
An example where there are five columns to be written out, each of which holds ten strings sorted alphabetically:
julia> using CSV, DataFrames, Random
julia> for i ∈ 1:5
val = sort([randstring(3) for _ ∈ 1:10])
CSV.write("test.csv", DataFrame(permutedims(val), :auto), append = true)
end
julia> CSV.read("test.csv", DataFrame; transpose = true, header = false)
10×5 DataFrame
Row │ Column1 Column2 Column3 Column4 Column5
│ String3 String3 String3 String3 String3
─────┼─────────────────────────────────────────────
1 │ 98g AW6 02L 0HL 10n
2 │ Anq Bgv 8JB 0jf 8RH
3 │ FCL D2n 8Z1 2wd O5N
4 │ SUf QwW FhK 7jk QfP
5 │ ewW Sd2 Jxw EEv XgW
6 │ mG9 Thi Tbk Lx1 cqi
7 │ mm5 jI6 WI8 QsI lbm
8 │ nEa ou5 bRs S3o sIF
9 │ u2w rnz hb1 TPh tJD
10 │ zKW tZh x2J bJb tPn
Here val is a column in the final table - 10 random strings of length 3, sorted alphabetically. I then put this vector in a DataFrame transposed, which means instead of one column of lenght 10, I get a table with 10 columns and one row:
julia> DataFrame(permutedims(val), :auto)
1×10 DataFrame
Row │ x1 x2 x3 x4 x5 x6 x7 x8 x9 x10
│ String String String String String String String String String String
─────┼────────────────────────────────────────────────────────────────────────────────
1 │ 3vh J4M JDu Y2P Zcb dLA dTy oU6 rhG tN2
the column names x1 to x10 come from the :auto kwarg, but are irrelevant here because CSV.write with append = true will ignore the header anyway.
Doing this in a loop I therefore end up with a 5 row, 10 column csv file. Reading this in with transpose = true will give me a 10x5 table, and header = false means that CSV will just assign Column1...Column5 as column names.