Export an array to a CSV file in Julia

Question

Given a (2d) array A how to export it into a CSV file with Julia?

Back in the older versions, I would write

writecsv( "FileName.csv",  A);

which would dump the array A into the given file. This, however, does not work in version >= 1.0. After some googling, I also tried to use the CSV module doing

f = open("test.csv", "a+");
CSV.write(f, A; delim = ',')

but this throws an error

ERROR: ArgumentError: no default `Tables.rows` implementation for type: Array{Int64,2}

(my array A was of type Int64).

Does anyone have a working solution for this most trivial question?

Lobar

Answer 1

You need to load DelimitedFiles module and now only writedlm function is supported.

So in order to write an array as CSV file use:

julia> using DelimitedFiles

julia> writedlm( "FileName.csv",  A, ',')

To get the same result with CSV.jl package use:

julia> using CSV, Tables

julia> CSV.write("FileName.csv",  Tables.table(A), writeheader=false)

as Matrix does not support Tables.jl interface so you need to wrap it with Tables.table.

Peursem

Not sure if this is always needed, but note that you may have to add the :auto argument, as in DataFrame(A, :auto). Bogumił, is this the newer practice? Thanks. Quote: "DataFrame constructor from a Matrix requires passing :auto as a second argument to automatically generate column names: DataFrame(matrix, :auto)" – Along

yes, now :auto is required. I updated the answer with the currently recommended practice - Tables.table which does not copy. – Pustulate

When I try this fix I get the error message MethodError: no method matching table(::Array{Int64, 3}). Is this because I can't write a 3d array to a .csv file? Is here any way in julia to write a 3d array to a .csv file? – Photography