将CSV标头和值转换为地图，其余转换为地图列表Elixir

Question

我有一个CSV文件

revenue,currency,date,random1,random2,random3
1.234,eur,2020-05-19,"random","random","random"
1.234,usd,2020-05-19,"random","random","random"
1.234,eur,2020-05-19,"random","random","random"
1.234,bng,2020-05-19,"random","random","random"
1.234,eur,2020-05-19,"random","random","random"
1.234,eur,2020-05-19,"random","random","random"
1.234,jpy,2020-05-19,"random","random","random"
1.234,cny,2020-05-19,"random","random","random"
1.234,chf,2020-05-19,"random","random","random"
1.234,eur,2020-05-19,"random","random","random"
1.234,eur,2020-05-19,"random","random","random"

上面的只是一个示例，但它可以有许多意想不到的列，前3列是常量，每个CSV都是相同的(头)。

我试图得到这些前3列的地图和其余列的地图列表。

我已经试过了，

"csvs/download.csv"
|> File.stream!()
|> NimbleCSV.RFC4180.parse_stream(skip_headers: false)
|> Stream.transform([], fn r, acc ->
{[Enum.zip(acc, r) |> Enum.into(%{})], acc}
end)
|> Enum.to_list()

这给了我一个空映射列表，

[%{}, %{}, %{}, %{}, %{}, %{}, %{}, %{}, %{}, %{}, %{}, %{}]

我的计划是像这样转换它，然后在一个列表中取前3个，其余的到另一个列表。但是第一部分不起作用。

任何帮助都太好了。解析后的预期结果是

[
%{revenue: revenue, currency: currency, date: date, rest: [%{anyname: any_data, anyname: any_data}]},
%{revenue: revenue, currency: currency, date: date, rest: [%{anyname: any_data, anyname: any_data}]}
....
]

我是这样做的:

data = NimbleCSV.RFC4180.parse_string(File.read("path_to_csv.csv"), skip_headers: false)
known_headers = ~w(revenue currency date)
[headers | content] = data
content
|> Enum.map(fn row ->
headers |> Enum.zip(row) |> Map.new |> Map.split(known_headers)
end)

无法得到预期的结果，但我知道可能有更好的解决方案。

Answer 1

问题是acc是一个空列表，压缩到空列表会导致每个步骤都是空列表。如果acc为空，则应该显式地启动它。

"csvs/download.csv"
|> File.stream!()
|> NimbleCSV.RFC4180.parse_stream(skip_headers: false)
|> Stream.transform([], fn 
r, [] -> {[], r}  # ⇐ THIS
r, acc -> {[acc |> Enum.zip(r) |> Map.new()], acc}
end)
|> Enum.to_list()

---

对结果进行重组，处理[acc |> Enum.zip(r) |> Map.new()]部分。例如，分割地图，如问题:

r, acc ->
{result, others} =
acc
|> Enum.zip(r)
|> Map.new()
|> Map.split(~w|revenue currency date|)
{[Map.put(result, :others, others)], acc}