template =
      "hi #name, you have scored #physics in physics, #chemistry in chemistry and #maths in maths"

input = """
    name,maths,chemistry,physics
    James Ortega,44,14,49
    Eula Garrett,26,74,16
    Emily Marsh,47,22,73
    Tommy Jenkins,37,54,55
    Ronnie Nash,54,04,31
"""

[headers] =
      input
      |> NimbleCSV.RFC4180.parse_string(skip_headers: false)
      |> Enum.take(1)

replacement_hs =
      headers
      |> Enum.map(fn header -> "#" <> header end)

input
|> NimbleCSV.RFC4180.parse_string(skip_headers: true)
|> Enum.map(fn row ->
      Enum.zip_reduce(row, replacement_hs, template, fn col_val, header, acc ->
        String.replace(acc, header, col_val)
    end)
end)

The only reasons to use NimbleCSV here is because sometimes there can be escaped separation characters and if you have a streamable source it’s just easier to get it working. Using @mindok example but with a string I would just map the headers into their replacement tokens ("#some_header") and then brute force the replacements unless it turned out to be slower than acceptable at which maybe compiling a custom regex could be faster.

Definitely use a CSV-parser. I just wanted to keep it simple.

I like your little template-engine, but maybe its not really beginner-friendly (and it doesn’t address the selection of the template by CSV header).

my solution with nimble

def load(csv) do
  [header | rows] = NimbleCSV.RFC4180.parse_string(csv, skip_headers: false)
  Enum.map(rows, fn row -> sentence(row, header) end)
end

defp sentence([name, email, balance], ["name", "email", "balance"]) do
  "#{name}, you owe us #{balance} this month. Please see your statement here #{email}"
end

defp sentence([other, header], ["other", "header"]) do
  "#{other}, ... #{header} ..."
end

@mnussbaumer’s solution is better because you don’t need to write code for the templates, could even put them in a json if you want. Just create a map header -> template from which to select the template you need.

Still not sure what you want, is it this?

test "sentences" do
  data = """
  name,email,balance
  Francis Waters,jolir@jalih.mz,$1810.08
  Ina Thomas,duzzigip@hizjos.cl,$5639.13
  George Cortez,siw@jijol.ma,$222.81
  Oscar Nguyen,ov@rici.nu,$7167.56
  Wayne Campbell,nad@tuj.jp,$964.14
  """
  
  rows = String.split(data, "\n")
  Enum.map(rows, fn line -> line |> String.split(",") |> sentence() end)
end


defp sentence([name, email, balance]) do
  "#{name}, you owe us #{balance} this month. Please see your statement here #{email}"
end
defp sentence(_), do: ""

["name, you owe us balance this month. Please see your statement here email",
 "Francis Waters, you owe us $1810.08 this month. Please see your statement here jolir@jalih.mz",
 "Ina Thomas, you owe us $5639.13 this month. Please see your statement here duzzigip@hizjos.cl",
 "George Cortez, you owe us $222.81 this month. Please see your statement here siw@jijol.ma",
 "Oscar Nguyen, you owe us $7167.56 this month. Please see your statement here ov@rici.nu",
 "Wayne Campbell, you owe us $964.14 this month. Please see your statement here nad@tuj.jp",
 ""]

Using Enum.take(1) on a stream to get the headers should be pretty efficient. Using Nimble CSV:

  alias NimbleCSV.RFC4180, as: CSV

 ...
 # Creates a list of header names
 [header] 
  = input_csv_stream 
    |> CSV.parse_stream(skip_headers: false) 
    |> Enum.take(1)

 # Then you can do what you need to with the main CSV. If you are a bit lazy (like me) you can zip
 # the header with the value into a map to allow easy lookup for processing your string template
 data 
  = input_csv_stream
    |> CSV.parse_stream(skip_headers: true)
    |> Stream.map(fn row -> Enum.zip(header, row) |> Enum.into(%{}) end)
    |> Stream.map(fn row_map -> template_wrangling_stuff(template, row_map) end)
    |> Enum.take(10) # or however you want to deal with the output

It takes about 1 sec to load and convert a 1.000.000 lines CSV.
So I’d just stick with the naive implementation for this one (and - having about 1 Billion revenue in that file - just buy a supercomputer to speed things up if need be).