CSV
RFC 4180 compliant CSV parsing and encoding for Elixir. Allows to specify other separators, so it could also be named: TSV. Why it is not idk, because of defaults I think.
Why do we want it?
It parses files which contain rows (in utf-8) separated by either commas or other separators.
If that's not enough reason to absolutely
When do we want it?
Now.
How do I get it?
Add
{:csv, "~> 2.3"}
to your deps in mix.exs
like so:
defp deps do
[
{:csv, "~> 2.3"}
]
end
Note: Elixir
1.1.0
is required for all versions above1.1.5
.
™️ update.
From 1.x to 2.x - the tasty 2.x has some nice new features like the separation between hair- and error-raising
decode!
and the zen of
decode
, better error messages
and an easier to understand codebase
for you to contribute.
The only thing you have to do to upgrade to 2.x is to change your calls to
decode
to decode!
,
and adjust your exceptions-catching code to catch the
right exceptions
still. But why not take full advantage and convert to
decode
and the new tuple stream?
You know you want it.
Great! How do I use it right now?
There are two interesting things you want to do regarding csvs - encoding end decoding.
Decoding
Do this to decode:
File.stream!("data.csv") |> CSV.decode
And you'll get a stream of row tuples:
[ok: ["a", "b"], ok: ["c", "d"]]
And, potentially error tuples:
[error: "Row has length 3 - expected length 2 on line 1", ok: ["c", "d"]]
Use the bang to decode! into a two-dimensional list, raising errors as they occur:
File.stream!("data.csv") |> CSV.decode!
Be sure to read more about decode
and its angry sibling decode!
Encoding
Do this to encode a table (two-dimensional list):
table_data |> CSV.encode
And you'll get a stream of lines ready to be written to an IO. So, this is writing to a file:
file = File.open!("test.csv", [:write, :utf8])
table_data |> CSV.encode |> Enum.each(&IO.write(file, &1))
⁉️
I have this file, but it's tab-separated Pass in another separator to the decoder:
File.stream!("data.csv") |> CSV.decode(separator: ?\t)
If you want to take revenge on whoever did this to you, encode with semicolons like this:
your_data |> CSV.encode(separator: ?;)
You can also specify headers when encoding, which will encode map values into the right place:
[%{"a" => "value!"}] |> CSV.encode(headers: ["z", "a"])
# ["z,a\\r\\n", ",value!\\r\\n"]
You'll surely appreciate some more info on encode
Polymorphic encoding
Make sure your data gets encoded the way you want - implement the CSV.Encode
protocol for whatever strange you wish to encode:
defimpl CSV.Encode, for: MyData do
def encode(%MyData{has: fun}, env \\ []) do
"so much #{fun}" |> CSV.Encode.encode(env)
end
end
Or similar.
Ensure performant encoding
The encoding protocol implements a fallback to Any for types where a simple call
o to_string
will provide unambiguous results. Protocol dispatch for the
fallback to Any is very slow when protocols are not consolidated, so make sure
you have consolidate_protocols: true
in your mix.exs
or you consolidate protocols manually for production in order
to get good performance.
There is more to know about everything
License
MIT
Contributions & Bugfixes are most welcome!
Please make sure to add tests. I will not look at PRs that are either failing or lowering coverage. Also, solve one problem at a time.