Elixir : how to display a structured data element? - csv

Question

I'm trying to parse a CSV file. Actually I have this code :
alias NimbleCSV.RFC4180, as: CSV
defmodule Siren do
def parseCSV do
IO.puts("Let's parse CSV file!")
stream = File.stream!("name.csv")
original_line = CSV.parse_stream(stream)
filter_line = Stream.filter(original_line, fn
["JeremyGuthrie" | _] -> true
_ -> false
end)
map = Stream.map(filter_line,
fn [name, team, position, height, weight, age] ->
%{name: name, team: team, position: position,
height: String.to_integer(height),
weight: String.to_integer(weight),
age: Float.parse(age) |> elem(0)
}
end)
end
end
According to my view I build a stream who handle each line of my name.csv file. With NimbleCSV library I parse this line and avoid the header line. Then, I filter each line to keep only the one corresponding to JeremyGuthrie. And finally I stock the line element into a structured data map. But now how to print just the name of my filter line : here JeremyGuthrie.
And I have an other question : I'm having some problems to filter my stream according to a number like an age, height or weight.
Here I apply Aleksei's advice with another code :
NimbleCSV.define(MyParser, separator: ";", escape: "\"")
defmodule Siren do
def parseCSV do
IO.puts("Let's parse CSV file!")
"ActeursEOF.csv"
|> File.stream!()
|> MyParser.parse_stream()
|> Stream.filter(fn
["RAZEL BEC" | _] -> true
["" | _] -> false
_ -> false
end)
|> Stream.map(fn [name, description, enr_competences] ->
%{name: name, description: description, enr_competences: enr_competences}
end)
|> Enum.to_list()
|> IO.inspect()
end
end
My output:
Compiling 1 file (.ex)
Let's parse CSV file!
[%{description: "Génie Civil", enr_competences: "Oui", name: "RAZEL BEC"}]
But now to close this subject I would to access and stock just the description for instance. And I don't see how to do that... And finally display this data.

Answer 1

Producing intermediate variables is redundant, in elixir we have Kernel.|>/2 aka pipe operator to pipe the functions’ output to the first argument of the next function.
"name.csv"
|> File.stream!()
|> CSV.parse_stream()
|> Stream.filter(fn
["JeremyGuthrie" | _] -> true
_ -> false
end)
|> Stream.map(fn
[name, team, position, height, weight, age] ->
%{name: name, team: team, position: position,
height: String.to_integer(height),
weight: String.to_integer(weight),
age: Float.parse(age) |> elem(0)
}
end)
|> Enum.to_list() # THIS
Note the last line in the chain. Streams are to be terminated to retrieve the result. Until the termination happens, it’s lazily constructed, but not evaluated at all. That makes it possible to e.g. produce and operate infinite streams.
Any greedy function from Enum module would do: Enum.take/2, or, as I pointed out above, Enum.to_list/1.
For the sake of reference, in the future, when you feel fully familiar with elixir, you might use Flow instead of Stream to parallelize mapping. For now (and for relatively small files) Stream is good enough.