I am trying to write an F# DataTable to csv (or output in a txt). The table I have is defined as follows:
let setup_report_tbl ( tbl : DataTable ) =
ignore( tbl.Columns.Add("business_date", typeof<System.Int32>) )
ignore( tbl.Columns.Add("ticker", typeof<System.String>) )
ignore( tbl.Columns.Add("price", typeof<System.String>) )
ignore( tbl.Columns.Add("rate", typeof<System.Boolean>) )
ignore( tbl.Columns.Add("range", typeof<System.Double>) )
My goal is to write this empty table with headers into a csv or txt. I'm new to F# and not quite sure where to start here, any help is appreciated thanks!
To write a DataTable as CSV, I would do something like this:
open System
open System.IO
open System.Data
let writeCsv (wtr : StreamWriter) (tbl : DataTable) =
let writeValues (values : seq<_>) =
String.Join(',', values)
|> wtr.WriteLine
tbl.Columns
|> Seq.cast<DataColumn>
|> writeValues
for row in tbl.Rows do
row.ItemArray |> writeValues
Note that I haven't done anything to check for special characters in the values, such commas or quotes.
Example:
let tbl = new DataTable()
setup_report_tbl tbl
tbl.Rows.Add(1, "moo", "baa", true, 2.0) |> ignore
use wtr = new StreamWriter(Console.OpenStandardOutput())
writeCsv wtr tbl
Output is:
business_date,ticker,price,rate,range
1,moo,baa,True,2
Update
To avoid compiler error, perhaps try this:
let writeValues (values : seq<_>) =
let s = String.Join(',', values)
wtr.WriteLine(s)
Note that s is a string, so there should be no ambiguity in which version of WriteLine is called.
If you wanted to use an existing library rather than writing your own CSV encoding (which may get tricky when you need to escape things), you could use Deedle which has an easy way to create data frame from a DataTable and save it to a CSV file:
#r "nuget: Deedle"
open Deedle
open System.Data
// Setup table using your function and add some data
let tbl = new DataTable()
setup_report_tbl tbl
tbl.Rows.Add(1, "very\",evil'ticker", "$42", false, 1.23)
// Turn it into a dataframe and save it
let df = Frame.ReadReader(tbl.CreateDataReader())
df.SaveCsv("C:/temp/test.csv")
As a bonus point, you could see if the data frame type from Deedle lets you do some of the other things you want to do with the data - but this depends on your scenario.
I'm trying to draw some boxes in Rascal and trying to give each box its own callback function. On entering the box with the mouse the corresponding string should get displayed in the text element (so hovering box1 should display box1 etc.).
However, at the moment the text does pop up but just displays "box3" for each of the 3 boxes.
Any ideas?
strings = ["box1", "box2", "box3"];
boxes = [ box(
size(100, 100),
onMouseEnter(void() {
output = s;
})
) | s <- strings];
render(hcat([
vcat(boxes),
text(str () {return output;})
]));
Good question, classical problem. The essence of the problem is that Rascal uses "non-capturing closures": this means that functions that are returned from another function share the same context. In your case this is the variable s introduced by s <- strings. This nearly always happens when you create function values in a loop (as you do here). The solution is to wrap another function layer around the returned function.
Here is a simple example:
list[int()] makeClosures()
= [ int() {return i;} | i <- [0,1,2]];
void wrong(){
lst = makeClosures();
println(lst[0]());
println(lst[1]());
println(lst[2]());
}
which will print surprisingly the values 2,2and2`. The solution is, as said, to introduce another function level:
int() makeClosure(int i)
= int() { return i;};
list[int()] makeClosuresOK()
= [ makeClosure(i) | i <- [0,1,2]];
void right(){
lst = makeClosuresOK();
println(lst[0]());
println(lst[1]());
println(lst[2]());
}
now calling right() will print 1, 2, and 3 as expected.
I leave it as an exercise how this is done in your example, but I am prepared to give a solution when you ask for it. Good luck!
i am new with f# , will be great if some 1 can help , nearly half a day gone solving this problem Thank you
module Certificate =
type T = {
Id: int
IsECert: bool
IsPrintCert: bool
CertifiedBy: string
Categories: Category.T list
}
let createPending now toZonedDateTime toBeCertifiedByName (job: Models.Job.T) (certificateType: Models.CertificateType.T) (pendingCertificate: Models.PendingCertificate.T) visualization (categories: Category.T list) =
let forCompletion = Models.PendingCertificate.getCertificateForCompletion pendingCertificate
{
Id = forCompletion.Id |> CertificateId.toInt
IsECert = Models.PendingCertificate.isECertificate pendingCertificate
IsPrintCert = Models.PendingCertificate.isPrintCertificate pendingCertificate
CertifiedBy = toBeCertifiedByName
Categories = categories}
i am getting an error in "Incomplete structured construct at or before this point"
Your formatting is all off. I will assume here that this is just a result of posting to StackOverflow, and your actual code is well indented.
The error comes from the definition of createPending: this function does not have a result. All its body consists of defining a forCompletion value, but there is nothing after it. Here's a simpler example that has the same problem:
let f x =
let y = 5
This function will produce the same error, because it also doesn't have a result. In F#, every function has to return something. The body cannot contain only definitions of helper functions or values. For example, I could fix my broken function above like this:
let f x =
let y = 5
x + y
This function first defines a helper value y, then adds it to its argument x, and returns the result.
> f 2
> 7
>
> f 0
> 5
How exactly you need to fix your function depends on what exactly you want it to mean. I can't help you here, because you haven't provided that information.
I am playing with records and list. Please, I want to know how to use one variable twice. When I assign any values into variable _list and after that I try rewrite this variable then raising error:
** exception error: no match of right hand side value
-module(hello).
-author("anx00040").
-record(car, {evc, type, color}).
-record(person, {name, phone, addresa, rc}).
-record(driver, {rc, evc}).
-record(list, {cars = [], persons = [], drivers = []} ).
%% API
-export([helloIF/1, helloCase/1, helloResult/1, helloList/0, map/2, filter/2, helloListCaA/0, createCar/3, createPerson/4, createDriver/2, helloRecords/0, empty_list/0, any_data/0, del_Person/1, get_persons/1, do_it_hard/0, add_person/2]).
createCar(P_evc, P_type, P_color) -> _car = #car{evc = P_evc, type = P_type, color = P_color}, _car
.
createPerson(P_name, P_phone, P_addres, P_rc) -> _person= #person{name = P_name, phone = P_phone, addresa = P_addres, rc = P_rc}, _person
.
createDriver(P_evc, P_rc) -> _driver = #driver{rc = P_rc, evc = P_evc}, _driver
.
empty_list() ->
#list{}.
any_data() ->
_car1 = hello:createCar("BL 4", "Skoda octavia", "White"),
_person1 = hello:createPerson("Eduard B.","+421 917 111 711","Kr, 81107 Bratislava1", "8811235"),
_driver1 = hello:createDriver(_car1#car.evc, _person1#person.rc),
_car2 = hello:createCar("BL 111 HK", "BMW M1", "Red"),
_person2 = hello:createPerson("Lenka M","+421 917 111 111","Krizn0, 81107 Bratislava1", "8811167695"),
_driver2 = hello:createDriver(_car2#car.evc, _person2#person.rc),
_car3 = hello:createCar("BL 123 AB", "Audi A1 S", "Black"),
_person3 = hello:createPerson("Stela Ba.","+421 918 111 711","Azna 20, 81107 Bratislava1", "8811167695"),
_driver3 = hello:createDriver(_car3#car.evc, _person3#person.rc),
_list = #list{
cars = [_car1,_car2,_car3],
persons = [_person1, _person2, _person3],
drivers = [_driver1, _driver2, _driver3]},
_list.
add_person(List, Person) ->
List#list{persons = lists:append([Person], List#list.persons) }.
get_persons(#list{persons = P}) -> P.
do_it_hard()->
empty_list(),
_list = add_person(any_data(), #person{name = "Test",phone = "+421Test", addresa = "Testova 20 81101 Testovo", rc =88113545}),
io:fwrite("\n"),
get_persons(add_person(_list, #person{name = "Test2",phone = "+421Test2", addresa = "Testova 20 81101 Testovo2", rc =991135455}))
.
But it raising error when i use variable _list twice:
do_it_hard()->
empty_list(),
_list = add_person(any_data(), #person{name = "Test",phone = "+421Test", addresa = "Testova 20 81101 Testovo", rc =88113545}),
_list =add_person(_list, #person{name = "Test2",phone = "+421Test2", addresa = "Testova 20 81101 Testovo2", rc =991135455}),
get_persons(_list)
.
In the REPL, it can be convenient to experiment with things while re-using variable names. There, you can do f(A). to have Erlang "forget" the current assignment of A.
1> Result = connect("goooogle.com").
{error, "server not found"}
2> % oops! I misspelled the server name
2> f(Result).
ok
3> Result = connect("google.com").
{ok, <<"contents of the page">>}
Note that this is only a REPL convenience feature. You can't do this in actual code.
In actual code, variables can only be assigned once. In a procedural language (C, Java, Python, etc), the typical use-case for reassignment is loops:
for (int i = 0; i < max; i++) {
conn = connect(servers[i]);
reply = send_data(conn);
print(reply);
}
In the above, the variables i, conn, and reply are reassigned in each iteration of the loop.
Functional languages use recursion to perform their loops:
send_all(Max, Servers) ->
send_loop(1, Max, Servers).
send_loop(Current, Max, _Servers) when Current =:= Max->
ok;
send_loop(Current, Max, Servers) ->
Conn = connect(lists:nth(Current, Servers)),
Reply = send_data(Conn),
print(Reply).
This isn't very idiomatic Erlang; I'm trying to make it mirror the procedural code above.
As you can see, I'm getting the same effect, but my assignments within a function are fixed.
As a side note, you are using a lot of variable names beginning with underscore. In Erlang this is a way of hinting that you will not be using the value of these variables. (Like in the above example, when I've reached the end of my list, I don't care about the list of servers.) Using a leading underscore as in your code turns off some useful compiler warnings and will confuse any other developers who look at your code.
In some situations it is convenient to use use SeqBind:
SeqBind is a parse transformation that auto-numbers all occurrences of these bindings following the suffix # (creating L#0, L#1, Req#0, Req#1) and so on.
Simple example:
...
-compile({parse_transform,seqbind}).
...
List# = lists:seq(0, 100),
List# = lists:filter(fun (X) -> X rem 2 == 0 end, List#)
...
I used google...
Erlang is a single-assignment language. That is, once a variable has been given a value, it cannot be given a different value. In this sense it is like algebra rather than like most conventional programming languages.
http://www.cis.upenn.edu/~matuszek/General/ConciseGuides/concise-erlang.html
I would like to display a directory structure using Gtk# widgets through F#, but I'm having a hard time figuring out how to translate TreeViews into F#. Say I had a directory structure that looks like this:
Directory1
SubDirectory1
SubDirectory2
SubSubDirectory1
SubDirectory3
Directory2
How would I show this tree structure with Gtk# widgets using F#?
EDIT:
gradbot's was the answer I was hoping for with a couple of exceptions. If you use ListStore, you loose the ability to expand levels, if you instead use :
let musicListStore = new Gtk.TreeStore([|typeof<String>; typeof<String>|])
you get a layout with expandable levels. Doing this, however, breaks the calls to AppendValues so you have to add some clues for the compiler to figure out which overloaded method to use:
musicListStore.AppendValues (iter, [|"Fannypack" ; "Nu Nu (Yeah Yeah) (double j and haze radio edit)"|])
Note that the columns are explicitly passed as an array.
Finally, you can nest levels even further by using the ListIter returned by Append Values
let iter = musicListStore.AppendValues ("Dance")
let subiter = musicListStore.AppendValues (iter, [|"Fannypack" ; "Nu Nu (Yeah Yeah) (double j and haze radio edit)"|])
musicListStore.AppendValues (subiter, [|"Some Dude"; "Some Song"|]) |> ignore
I'm not exactly sure what you're looking for but here is a translated example from their tutorials. It may help you get started. Image taken from tutorial site.
I think the key to a multi-level tree view is to append values to values, iter in this line musicListStore.AppendValues (iter, "Fannypack", "Nu Nu (Yeah Yeah) (double j and haze radio edit)") |> ignore
// you will need to add these references gtk-sharp, gtk-sharp, glib-sharp
// and set the projects running directory to
// C:\Program Files (x86)\GtkSharp\2.12\bin\
module SOQuestion
open Gtk
open System
let main() =
Gtk.Application.Init()
// Create a Window
let window = new Gtk.Window("TreeView Example")
window.SetSizeRequest(500, 200)
// Create our TreeView
let tree = new Gtk.TreeView()
// Add our tree to the window
window.Add(tree)
// Create a column for the artist name
let artistColumn = new Gtk.TreeViewColumn()
artistColumn.Title <- "Artist"
// Create the text cell that will display the artist name
let artistNameCell = new Gtk.CellRendererText()
// Add the cell to the column
artistColumn.PackStart(artistNameCell, true)
// Create a column for the song title
let songColumn = new Gtk.TreeViewColumn()
songColumn.Title <- "Song Title"
// Do the same for the song title column
let songTitleCell = new Gtk.CellRendererText()
songColumn.PackStart(songTitleCell, true)
// Add the columns to the TreeView
tree.AppendColumn(artistColumn) |> ignore
tree.AppendColumn(songColumn) |> ignore
// Tell the Cell Renderers which items in the model to display
artistColumn.AddAttribute(artistNameCell, "text", 0)
songColumn.AddAttribute(songTitleCell, "text", 1)
let musicListStore = new Gtk.ListStore([|typeof<String>; typeof<String>|])
let iter = musicListStore.AppendValues ("Dance")
musicListStore.AppendValues (iter, "Fannypack", "Nu Nu (Yeah Yeah) (double j and haze radio edit)") |> ignore
let iter = musicListStore.AppendValues ("Hip-hop")
musicListStore.AppendValues (iter, "Nelly", "Country Grammer") |> ignore
// Assign the model to the TreeView
tree.Model <- musicListStore
// Show the window and everything on it
window.ShowAll()
// add event handler so Gtk will exit
window.DeleteEvent.Add(fun _ -> Gtk.Application.Quit())
Gtk.Application.Run()
[<STAThread>]
main()