How do I print out year with average number recursively in F#? - recursion

Question

Okay, so I have approached this headache for a couple days by trying to figure out how to print out year with average number from per line in my text file. I asked this similar question a couple days ago so basically I'm asking the same question, How do I print out lines recursively from a text file along with the average value of total elements from per line?
this goes on. However, I have created several functions. Now, here is my new question. Why does my program's output looks like this in the picture below? I have commented out a couple questions in my codes. I have been expecting to have output like
2010: 3.5788888
2009: 4.697858
This list goes on recursively.
here is my updated codes:
let ReadFile filename =
[ for line in System.IO.File.ReadLines(filename) -> line ]
let ParseLine (line:string) =
let strings = line.Split('\t')
let strlist = Array.toList(strings)
let year = System.Int32.Parse(strlist.Head)
let values = List.map System.Double.Parse strlist.Tail
(year, values)
let rec print (year, values) =
if values = [] then
()
else
printfn "%A: %A" year values.Head
print (year, values.Tail)
let avg (values:double list) = //this function can compute the average, but it wont work when I do in main, print(firstYear, avg (firstYear1))
let rec sum values accum =
match values with
| [] -> accum
| head :: tail -> sum tail (accum + head/12.0)
sum values 0.0
let rec sum (year, values:double list) =
if values = [] then
0.0
else
values.Head + sum (year, values.Tail)
[<EntryPoint>]
let main argv =
// read entire file as list of strings:
let file = ReadFile "rainfall-midway.txt"
printfn "** Rainfall Analysis Program **"
printfn ""
// let's parse first line into tuple (year, list of rainfall values),
// and then print for debugging:
let (year, values) = ParseLine file.Head
let firstYear = file.Head
let firstYear1 = file.Tail
//let data = List.map ParseLine file //I know map would be the key, but how does this work with year and its elements?
//let firstYear = data.Head
//let firstYear = data.Head
//print firstYear
print (firstYear, firstYear1)
//let S = sum firstYear
//printfn "%A" S
//let A = S / 12.0
//printfn "%A" A
// done:
printfn ""
printfn ""
0 // return 0 => success

Answer 1

The code you have is actually quite close to giving you the data you expect. There are a couple changes you could make to simplify things.
First to answer your question
Why does my program's output looks like this in the picture below?
This is because you are printing out the year and all of the parsed values (this doesn't match the code which just prints out the file). An easy way to resolve this is to have the ParseLine function calculate the average. You will need to move the avg prior to the ParseLine function but that should not be a problem.
let avg (values:double list) =
let rec sum values accum =
match values with
| [] -> accum
| head :: tail -> sum tail (accum + head/12.0)
sum values 0.0
let ReadFile filename =
[ for line in System.IO.File.ReadLines(filename) -> line ]
let ParseLine (line:string) =
let strings = line.Split('\t')
let strlist = Array.toList(strings)
let year = System.Int32.Parse(strlist.Head)
let values = List.map System.Double.Parse strlist.Tail
(year, avg values) // calculate avg here
Once that is done, you can use a map to run ParseLine on all lines from the file.
let result = file |> List.map ParseLine
Then to print out the results you need only iterate through the result list.
result |> List.iter(fun (year, avgRainfall) -> printfn "%i: %f" year avgRainfall)
That said we could just remove the sum and avg functions altogether and use fold instead in our ParseLine function.
let ParseLine (line:string) =
let strings = line.Split('\t')
let strlist = Array.toList(strings)
let year = System.Int32.Parse(strlist.Head)
year, (strlist.Tail |> List.fold(fun state el -> (System.Double.Parse el + state)) 0.0) / float strlist.Tail.Length
If you don't want to change the ParseLine function then you can do the following:
let result = file |> List.map(fun el ->
let (year, values) = ParseLine el
(year, avg values))